Implementing BGP Flowspec

Flowspec specifies procedures for the distribution of flow specification rules via BGP and defines procedure to encode flow specification rules as Border Gateway Protocol Network Layer Reachability Information (BGP NLRI) which can be used in any application. It also defines application for the purpose of packet filtering in order to mitigate (distributed) denial of service attacks.


Note

For more information about BGP Flowspec and complete descriptions of the BGP Flowspec commands listed in this module, see the BGP Flowspec Commands chapter in the Routing Command Reference for Cisco NCS 6000 Series Routers.

Feature History for Implementing BGP Flowspec

Release 5.2.4

This feature was introduced.

BGP Flow Specification

The BGP flow specification (flowspec) feature allows you to rapidly deploy and propagate filtering and policing functionality among a large number of BGP peer routers to mitigate the effects of a distributed denial-of-service (DDoS) attack over your network.

In traditional methods for DDoS mitigation, such as RTBH (remotely triggered blackhole), a BGP route is injected advertising the website address under attack with a special community. This special community on the border routers sets the next hop to a special next hop to discard/null, thus preventing traffic from suspect sources into your network. While this offers good protection, it makes the Server completely unreachable.

BGP flowspec, on the other hand, allows for a more granular approach and lets you effectively construct instructions to match a particular flow with source, destination, L4 parameters and packet specifics such as length, fragment and so on. Flowspec allows for a dynamic installation of an action at the border routers to either:

  • Drop the traffic

  • Inject it in a different VRF for analysis or

  • Allow it, but police it at a specific defined rate

Thus, instead of sending a route with a special community that the border routers must associate with a next hop to drop in their route policy language, BGP flowspec sends a specific flow format to the border routers instructing them to create a sort of ACL with class-map and policy-map to implement the rule you want advertised. In order to accomplish this, BGP flowspec adds a new NLRI (network layer reachability information) to the BGP protocol. Information About Implementing BGP Flowspec provides details on flow specifications, supported matching criteria and traffic filtering action.

The BGP Flowspec feature cannot coexist with MAP-E and PBR on a given interface. If you configure BGP Flowspec with PBR, the router does not display any error or system message. The router ignores the BGP-FS configuration and the feature will not function.

Limitations

These limitations apply for BGP flowspec:

  • For in-service software upgrade (ISSU), there is no support for zero packet loss (ZPL) for BGP Flowspec traffic.

  • Flowspec is not supported on subscriber and satellite interfaces.

  • A maximum of five multi-value range can be specified in a flowspec rule.

  • A mix of address families is not allowed in flowspec rules.

  • In multiple match scenario, only the first matching flowspec rule will be applied.

  • QoS takes precedence over BGP flowspec.

BGP Flowspec Conceptual Architecture

In this illustration, a Flowspec router (controller) is configured on the Provider Edge with flows (match criteria and actions). The Flowspec router advertises these flows to the other edge routers and the AS (that is, Transit 1, Transit 2 and PE). These transit routers then install the flows into the hardware. Once the flow is installed into the hardware, the transit routers are able to do a lookup to see if incoming traffic matches the defined flows and take suitable action. The action in this scenario is to 'drop' the DDoS traffic at the edge of the network itself and deliver only clean and legitimate traffic to the Customer Edge.

The ensuing section provides an example of the CLI configuration of how flowspec works. First, on the Flowspec router you define the match-action criteria to take on the incoming traffic. This comprises the PBR portion of the configuration. The service-policy type defines the actual PBR policy and contains the combination of match and action criteria which must be added to the flowspec. In this example, the policy is added under address-family IPv4, and hence it is propagated as an IPv4 flowspec rule. 


Flowspec router CLI example:

class-map type traffic match-all cm1
     match source-address ipv4 100.0.0.0/24

policy-map type pbr pm1
    class type traffic cm1
      drop


flowspec
    address-family ipv4
       service-policy type pbr pm0 

Transient router CLI: 

flowspec
    address-family ipv4
    			service-policy type pbr pm1

For detailed procedural information and commands used for configuring Flowspec, see How to Configure BGP Flowspec.

Information About Implementing BGP Flowspec

To implement BGP Flowspec, you need to understand the following concepts:

Flow Specifications

A flow specification is an n-tuple consisting of several matching criteria that can be applied to IP traffic. A given IP packet is said to match the defined flow if it matches all the specified criteria. A given flow may be associated with a set of attributes, depending on the particular application; such attributes may or may not include reachability information (that is, NEXT_HOP).

Every flow-spec route is effectively a rule, consisting of a matching part (encoded in the NLRI field) and an action part (encoded as a BGP extended community). The BGP flowspec rules are converted internally to equivalent C3PL policy representing match and action parameters. The match and action support can vary based on underlying platform hardware capabilities. Supported Matching Criteria and Actions and Traffic Filtering Actions provides information on the supported match (tuple definitions) and action parameters.

Supported Matching Criteria and Actions

A Flow Specification NLRI type may include several components such as destination prefix, source prefix, protocol, ports, and so on. This NLRI is treated as an opaque bit string prefix by BGP. Each bit string identifies a key to a database entry with which a set of attributes can be associated. This NLRI information is encoded using MP_REACH_NLRI and MP_UNREACH_NLRI attributes. Whenever the corresponding application does not require Next-Hop information, this is encoded as a 0-octet length Next Hop in the MP_REACH_NLRI attribute and ignored on receipt. The NLRI field of the MP_REACH_NLRI and MP_UNREACH_NLRI is encoded as a 1- or 2-octet NLRI length field followed by a variable-length NLRI value. The NLRI length is expressed in octets.

The Flow specification NLRI-type consists of several optional sub-components. A specific packet is considered to match the flow specification when it matches the intersection (AND) of all the components present in the specification. The following are the supported component types or tuples that you can define:

Table 1. Tuple definition possibilities

BGP Flowspec NLRI type

QoS match fields

Description and Syntax Construction

Value input method

Type 1

IPv4 Destination address

Defines the destination prefix to match. Prefixes are encoded in the BGP UPDATE messages as a length in bits followed by enough octets to contain the prefix information.

Encoding: <type (1 octet), prefix length (1 octet), prefix>

Syntax:

match destination-address {ipv4} address/mask length

Prefix length

Type 2

IPv4 Source address

Defines the source prefix to match.

Encoding: <type (1 octet), prefix-length (1 octet), prefix>

Syntax:

match source-address {ipv4} address/mask length

Prefix length

Type 3

IPv4 last next header Protocol

Contains a set of {operator, value} pairs that are used to match the IP protocol value byte in IP packets.

Encoding: <type (1 octet), [op, value]+>

Syntax:

Type 3: match protocol { protocol-value | min-value - max-value}

Multi value range

Type 4

IPv4 source or destination port

Defines a list of {operation, value} pairs that matches source or destination TCP/UDP ports. Values are encoded as 1- or 2-byte quantities. Port, source port, and destination port components evaluate to FALSE if the IP protocol field of the packet has a value other than TCP or UDP, if the packet is fragmented and this is not the first fragment, or if the system in unable to locate the transport header.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match source-port { source-port-value | min-value - max-value}

match destination-port { destination-port-value | min-value - max-value}

Multi value range

Type 5

IPv4 destination port

Defines a list of {operation, value} pairs used to match the destination port of a TCP or UDP packet. Values are encoded as 1- or 2-byte quantities.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match destination-port {destination-port-value | [min-value - max-value]}

Multi value range

Type 6

IPv4 Source port

Defines a list of {operation, value} pairs used to match the source port of a TCP or UDP packet. Values are encoded as 1- or 2-byte quantities.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match source-port {source-port-value | [min-value - max-value]}

Multi value range

Type 7

IPv4 ICMP type

Defines a list of {operation, value} pairs used to match the type field of an ICMP packet. Values are encoded using a single byte. The ICMP type and code specifiers evaluate to FALSE whenever the protocol value is not ICMP.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match { ipv4} icmp-type {value | min-value - max-value}

Single value

Note

 
Multi value range is not supported.

Type 8

IPv4 ICMP code

Defines a list of {operation, value} pairs used to match the code field of an ICMP packet. Values are encoded using a single byte.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match { ipv4} icmp-code {value | min-value - max-value}

Single value

Note

 
Multi value range is not supported.

Type 9

IPv4 TCP flags (2 bytes include reserved bits)

Note

 
Reserved and NS bit not supported

Bitmask values can be encoded as a 1- or 2-byte bitmask. When a single byte is specified, it matches byte 13 of the TCP header, which contains bits 8 through 15 of the 4th 32-bit word. When a 2-byte encoding is used, it matches bytes 12 and 13 of the TCP header with the data offset field having a "don't care" value. As with port specifier, this component evaluates to FALSE for packets that are not TCP packets. This type uses the bitmask operand format, which differs from the numeric operator format in the lower nibble.

Encoding: <type (1 octet), [op, bitmask]+>

Syntax:

match tcp-flag value bit-mask mask_value

Bit mask

Type 10

IPv4 Packet length

Match on the total IP packet length (excluding Layer 2, but including IP header). Values are encoded using 1- or 2-byte quantities.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match packet length { packet-length-value | min-value - max-value}

Multi value range

Type 11

IPv4 DSCP

Defines a list of {operation, value} pairs used to match the 6-bit DSCP field. Values are encoded using a single byte, where the two most significant bits are zero and the six least significant bits contain the DSCP value.

Encoding: <type (1 octet), [op, value]+>

Syntax:

match dscp { dscp-value | min-value - max-value}

Multi value range

Type 12

IPv4 Fragmentation bits

Note

 

IPv6 BGP flowspec does not supports Type 12 NRLI.

Identifies a fragment-type as the match criterion for a class map.

Encoding: <type (1 octet), [op, bitmask]+>

Syntax:

match fragment type [is-fragment]

Bit mask

In a given flowspec rule, multiple action combinations can be specified without restrictions.


Note
Redirect IP Nexthop is only supported in default VRF cases.

Traffic Filtering Actions provides information on the actions that can be associated with a flow. How to Configure BGP Flowspec explains the procedure to configure BGP flowpsec with the required tuple definitions and action sequences.

Traffic Filtering Actions

The default action for a traffic filtering flow specification is to accept IP traffic that matches that particular rule. You can use the following extended community values to specify particular actions:

Type

Extended Community

PBR Action

Description

0x8006

traffic-rate 0

traffic-rate <rate>

Drop

Police

Traffic-rate extended community is a non-transitive extended community across the autonomous system boundary. It uses the following extended community encoding:

You can assign the first two octets that carry the 2-octet id from a 2-byte autonomous system number. When a 4-byte autonomous system number is locally present, you can use the 2 least significant bytes of such an autonomous system number. This value is purely informational. The remaining 4 octets carry the rate information in IEEE floating point [IEEE.754.1985] format, units being bytes per second. A traffic-rate of 0 causes discarding of all traffic for the particular flow.

Command syntax

police rate < > | drop

0x8008

redirect-vrf

Redirect VRF

Redirect extended community redirects the traffic to a VRF routing instance that lists the specified route-target in its import policy. If several local instances match this criteria, the choice between them is local matter (for example, you can elect the instance with the lowest Route Distinguisher value). This extended community uses the same encoding as the Route Target extended community [RFC4360].

Command syntax based on route-target

redirect {ipv4} extcommunity rt <route_target_string>

0x8009

traffic-marking

Set DSCP

Traffic marking extended community instructs a system to modify the differentiated service code point (DSCP) bits of a transiting IP packet to the corresponding value. RFC 5575 encodes the extended community as a sequence. It is a sequence of 5 zero bytes followed by the DSCP value encoded in the 6 least significant bits of the sixth byte.

Command syntax

set dscp <6-bit value>

set ipv4 traffic-class <8-bit value>

0x0800

Redirect IP NH

Redirect IPv4 Nexthop

Redirect IP Next-Hop extended community announces the availability of one or more flowspec Network Layer Reachability Information (NLRI). When a BGP speaker receives an UPDATE message with the redirect-to-IP extended community, it creates a traffic-filtering rule for every flow-spec NLRI in the message that has this path as its best path. The filter entry matches the IP packets that BGP describes in the NLRI field. BGP specifies an IPv4 address in the Network Address of Next-Hop field of the associated Multiprotocol Reachable NLRI (MP_REACH_NLRI) The filter entry redirects the IP packets or copies them toward that address.

Note

 
The redirect-to-IP extended community is valid with any other set of flow-spec extended communities. If the set includes a redirect-to-VRF extended community (type 0x8008), the filter ignores the redirect-to-IP extended community.

Command syntax

redirect {ipv4} next-hop <ipv4 address> {ipv4 address}

Configure a Class Map explains how you can configure specific match criteria for a class map.

BGP Flowspec Client-Server (Controller) Model and Configuration

The BGP Flowspec model comprises of a Client and a Server (Controller). The Controller is responsible for sending or injecting the flowspec NRLI entry. The client (acting as a BGP speaker) receives that NRLI and programs the hardware forwarding to act on the instruction from the Controller. An illustration of this model is provided below.

BGP Flowspec Client

Here, the Controller on the left-hand side injects the flowspec NRLI, and the client on the right-hand side receives the information, sends it to the flowspec manager, configures the ePBR (Enhance Policy-based Routing) infrastructure, which in turn programs the hardware from the underlaying platform in use.

BGP Flowspec Controller

The Controller is configured using CLI to provide that entry for NRLI injection.

BGP Flowspec Configuration

  • BGP-side: You must enable the new address family for advertisement. This procedure is applicable for both the Client and the Controller. Enable Flowspec on BGP Side explains the procedure.

    Client-side: No specific configuration, except availability of a flowspec-enabled peer.

  • Controller-side: This includes the policy-map definition and the association to the ePBR configuration consists of two procedures: the class definition, and using that class in ePBR to define the action. The following topics explain the procedure:

How to Configure BGP Flowspec

Use the following procedures to enable and configure the BGP flowspec feature:


Note
To save configuration changes, you must commit changes when the system prompts you.

Enable Flowspec on BGP Side

You must enable the address family for propagating the BGP flowspec policy on both the Client and Server using the following steps:

SUMMARY STEPS

  1. configure
  2. router bgp as-number
  3. address-family { ipv4 | vpnv4 } flowspec
  4. exit
  5. neighbor ip-address
  6. remote-as as-number
  7. address-family { ipv4 } flowspec

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | vpnv4 } flowspec

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 flowspec

Specifies either the IPv4, vpn4 address family and enters address family configuration submode, and initializes the global address family for flowspec policy mapping.

Step 4

exit

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# exit

Returns the router to BGP configuration mode.

Step 5

neighbor ip-address

Example:
RP/0/RP0/CPU0:router(config-bgp)#neighbor 192.0.2.1

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 6

remote-as as-number

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#remote-as 100

Assigns a remote autonomous system number to the neighbor.

Step 7

address-family { ipv4 } flowspec

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 flowspec

Specifies an address family and enters address family configuration submode, and initializes the global address family for flowspec policy mapping.

Configure a Class Map

In order to associate the ePBR configuration to BGP flowspec you must perform these sub-steps: define the class and use that class in ePBR to define the action. The steps to define the class include:

SUMMARY STEPS

  1. configure
  2. class-map [type traffic] [match-all] class-map-name
  3. match match-statement
  4. end-class-map

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Step 2

class-map [type traffic] [match-all] class-map-name

Example:

RP/0/RP0/CPU0:router(config)# class-map type traffic match all classc1

Creates a class map to be used for matching packets to the class whose name you specify and enters the class map configuration mode. If you specify match-any , one of the match criteria must be met for traffic entering the traffic class to be classified as part of the traffic class. This is the default. If you specify match-all , the traffic must match all the match criteria.

Step 3

match match-statement

Example:

RP/0/RP0/CPU0:router(config-cmap)# match protocol ipv4 1 60

Configures the match criteria for a class map on the basis of the statement specified. Any combination of tuples 1-13 match statements can be specified here. The tuple definition possibilities include:

  • Type 1: match destination-address {ipv4} address/mask length

  • Type 2: match source-address {ipv4} address/mask length

  • Type 3: match protocol { protocol-value | min-value - max-value}

  • Type 4: Create two class-maps: one with source-port and another with destination-port:

    • match source-port { source-port-value | min-value - max-value}

    • match destination-port { destination-port-value | min-value - max-value}

      Note

       
      These are applicable only for TCP and UDP protocols.

  • Type 5: match destination-port {destination-port-value | [min-value - max-value]}

  • Type 6: match source-port {source-port-value | [min-value - max-value]}

  • Type 7: match { ipv4} icmp-code {value | min-value - max-value}

  • Type 8: match { ipv4} icmp-type {value | min-value - max-value}

  • Type 9: match tcp-flag value bit-mask mask_value

  • Type 10: match packet length { packet-length-value | min-value - max-value} }

  • Type 11: match dscp { dscp-value | min-value - max-value}

  • Type 12: match fragment-type { is-fragment }

  • Type 13: match ipv4 flow-label { value | min-value - max-value}

>

Step 4

end-class-map

Example:

RP/0/RP0/CPU0:router(config-cmap)# end-class-map

Ends the class map configuration and returns the router to global configuration mode.

What to do next

Associate the class defined in this procedure to a PBR policy .

Define Policy Map

This procedure helps you define a policy map and associate it with traffic class you configured previously in Configure a Class Map .

SUMMARY STEPS

  1. configure
  2. policy-map type pbr policy-map
  3. class class-name
  4. class type traffic class-name
  5. action
  6. exit
  7. end-policy-map

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

policy-map type pbr policy-map

Example:

RP/0/RP0/CPU0:router(config)# policy-map type pbr policyp1

Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy and enters the policy map configuration mode.

Step 3

class class-name

Example:

RP/0/RP0/CPU0:router(config-pmap)# class class1

Specifies the name of the class whose policy you want to create or change.

Step 4

class type traffic class-name

Example:

RP/0/RP0/CPU0:router(config-pmap)# class type traffic classc1

Associates a previously configured traffic class with the policy map, and enters control policy-map traffic class configuration mode.

Step 5

action

Example:

RP/0/RP0/CPU0:router(config-pmap-c)# set dscp 5
Define extended community actions as per your requirement. The options include:

  • Traffic rate: police rate rate

  • Redirect VRF: redirect { ipv4 } extcommunity rt route_target_string

  • Traffic Marking: set { dscp rate | destination-address {ipv4} 8-bit value}

  • Redirect IP NH: redirect { ipv4 } nexthop ipv4 address { ipv4 address}

Traffic Filtering Actions provides conceptual information on these extended community actions.

Step 6

exit

Example:

RP/0/RP0/CPU0:router(config-pmap-c)# exit

Returns the router to policy map configuration mode.

Step 7

end-policy-map

Example:

RP/0/RP0/CPU0:router(config-cmap)# end-policy-map

Ends the policy map configuration and returns the router to global configuration mode.

What to do next

Perform VRF and flowspec policy mapping for distribution of flowspec rules using the procedure explained in Link Flowspec to PBR Policies

Link Flowspec to PBR Policies

For BGP flowspec, a PBR policy is applied on a per VRF basis, and this policy is applied on all the interfaces that are part of the VRF. If you have already configured a PBR policy on an interface, it will not be overwritten by the BGP flowspec policy. If you remove the policy from an interface, PBR infrastructure will automatically apply BGP flowspec policy on it, if one was active at the VRF level.

Note

At a time only one PBR policy can be active on an interface.

SUMMARY STEPS

  1. configure
  2. flowspec
  3. local-install interface-all
  4. address-family ipv4
  5. local-install interface-all
  6. service-policy type pbr policy-name
  7. Use the commit or end command.
  8. exit
  9. show flowspec { afi-all | client | ipv4 | summary | vrf

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

flowspec

Example:

RP/0/RP0/CPU0:router(config)# flowspec

Enters the flowspec configuration mode.

Step 3

local-install interface-all

Example:

RP/0/RP0/CPU0:router(config-flowspec)# local-install interface-all

(Optional) Installs the flowspec policy on all interfaces.

Step 4

address-family ipv4

Example:

RP/0/RP0/CPU0:router(config-flowspec)# address-family ipv4

Specifies either an IPv4 address family and enters address family configuration submode.

Step 5

local-install interface-all

Example:

RP/0/RP0/CPU0:router(config-flowspec-af)# local-install interface-all

(Optional) Installs the flowspec policy on all interfaces under the subaddress family.

Step 6

service-policy type pbr policy-name

Example:

RP/0/RP0/CPU0:router(config-flowspec-af)# service-policy type pbr policys1

Attaches a policy map to an IPv4 interface to be used as the service policy for that interface.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 8

exit

Example:

RP/0/RP0/CPU0:router(config-flowspec-vrf-af)# exit

Returns the router to flowspec configuration mode.

Step 9

show flowspec { afi-all | client | ipv4 | summary | vrf

Example:

RP/0/RP0/CPU0:routershow flowspec vrf vrf1 ipv4 summary

(Optional) Displays flowspec policy applied on an interface.

Verify BGP Flowspec

Use these different show commands to verify your flowspec configuration. For instance, you can use the associated flowspec and BGP show commands to check whether flowspec rules are present in your table, how many rules are present, the action that has been taken on the traffic based on the flow specifications you have defined and so on.

SUMMARY STEPS

  1. show processes flowspec_mgr location all
  2. show flowspec summary
  3. show flowspec vrf vrf_name | all { afli-all | ipv4 }
  4. show bgp ipv4 flowspec
  5. show pbr-pal ipolicy all location node-id

DETAILED STEPS

  Command or Action Purpose

Step 1

show processes flowspec_mgr location all

Example:

# show processes flowspec_mgr location all
node:      node0_3_CPU0
-------------------------------------------------------------------------
Job Id: 10                   
PID: 43643169
Executable path: /disk0/iosxr-fwding-5.2.CSC33695-015.i/bin/flowspec_mgr
Instance #: 1
Version ID: 00.00.0000
Respawn: ON
Respawn count: 331
Max. spawns per minute: 12
Last started: Wed Apr  9 10:42:13 2014
Started on config: cfg/gl/flowspec/
Process group: central-services core: MAINMEM 
startup_path: /pkg/startup/flowspec_mgr.startup
Ready: 1.113s
Process cpu time: 0.225 user, 0.023 kernel, 0.248 total
JID   TID CPU Stack pri state    TimeInState    HR:MM:SS:MSEC   NAME
1082   1    0  112K  10 Receive    2:50:23:0508  0:00:00:0241 flowspec_mgr
1082   2    1  112K  10 Sigwaitinfo 2:52:42:0583   0:00:00:0000 flowspec_mgr

Specifies whether the flowspec process is running on your system or not. The flowspec manager is responsible for creating, distributing and installing the flowspec rules on the hardware.

Step 2

show flowspec summary

Example:

# show flowspec summary

FlowSpec Manager Summary:
  Tables:                          2
  Flows:                           1
RP/0/3/CPU0:RA01_R4#

Provides a summary of the flowspec rules present on the entire node. In this example, IPv4 has been enabled, and a single flow has been defined across the entire table.

Step 3

show flowspec vrf vrf_name | all { afli-all | ipv4 }

Example:


# show flowspec vrf default ipv4 summary

Flowspec VRF+AFI table summary:
VRF: default
  AFI: IPv4
    Total Flows:              1
    Total Service Policies:   1
RP/0/3/CPU0:RA01_R4#
---------------------------------------------------

# show flowspec vrf all afi-all summary

Flowspec VRF+AFI table summary:
VRF: default
  AFI: IPv4
    Total Flows:              1
    Total Service Policies:   1

--------------------------------------------------
# show flowspec vrf default ipv4 Dest:110.1.1.0/24,
Source:10.1.1.0/24,DPort:>=120&<=130,
SPort:>=25&<=30,DSCP:=30 detail

AFI: IPv4
 Flow           :Dest:110.1.1.0/24,Source:10.1.1.0/24,
DPort:>=120&<=130,SPort:>=25&<=30,DSCP:=30
  Actions       :Traffic-rate: 0 bps  (bgp.1)
  Statistics                        (packets/bytes)
   Matched             :                   0/0
   Transmitted         :                   0/0
   Dropped             :                   0/0

In order to obtain more granular information on the flowspec, you can filter the show commands based on a particular address-family or by a specific VRF name. In this example, 'vrf default' indicates that the flowspec has been defined on the default table. The 'IPv4 summary' shows the IPv4 flowspec rules present on that default table. 'VRF all' displays information across all the VRFs configured on the table and afli-all displays information for all address families.

The detail option displays the 'Matched', 'Transmitted, ' and 'Dropped' fields. These can be used to see if the flowspec rule you have defined is in action or not. If there is any traffic that takes this match condition, it indicates if any action has been taken (that is, how many packets were matched and whether these packets have been transmitted or dropped.

Step 4

show bgp ipv4 flowspec

Example:

# show bgp ipv4 flowspec Dest:110.1.1.0/24,Source:10.1.1.0/24,
DPort:>=120&<=130,SPort:>=25&<=30,DSCP:=30/208
BGP routing table entry for Dest:110.1.1.0/24,
Source:10.1.1.0/24,Proto:=47,DPort:>=120&<=130,SPort:>=25&<=30,DSCP:=30/208
<snip>
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.3
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.3
  Local
    0.0.0.0 from 0.0.0.0 (3.3.3.3)
      Origin IGP, localpref 100, valid, redistributed, best, group-best
      Received Path ID 0, Local Path ID 1, version 42
      Extended community: FLOWSPEC Traffic-rate:100,0

Use this command to verify if a flowspec rule configured on the controller router is available on the BGP side. In this example, 'redistributed' indicates that the flowspec rule is not internally originated, but one that has been redistributed from the flowspec process to BGP. The extended community (BGP attribute used to send the match and action criteria to the peer routers) you have configured is also displayed here. In this example, the action defined is to rate limit the traffic.

Step 5

show pbr-pal ipolicy all location node-id

On platform dependent devices, use this command to verify if a flowspec rule configured on the controller router is available on the BGP side.

Preserving Redirect Nexthop

You can explicitly configure redirect nexthop as part of the route specification. Redirect nexthop is encoded as the MP_REACH nexthop in the BGP flowspec NLRI along with the associated extended community. Recipient of such a flowspec route redirects traffic as per FIB lookup for the redirect nexthop, the nexthop can possibly resolve over IP or MPLS tunnel. As the MP_REACH nexthop can be overwritten at a eBGP boundary, for cases where the nexthop connectivity spans multiple AS's, the nexthop can be preserved through the use of the unchanged knob.

SUMMARY STEPS

  1. configure
  2. router bgp as-number
  3. neighbor ip-address
  4. address-family { ipv4 }
  5. flowspec next-hop unchanged

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config)# router bgp 100 neighbor 1.1.1.1

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

address-family { ipv4 }

Example:


RP/0/RP0/CPU0:router(config-bgp)# router bgp 100 neighbor 1.1.1.1 address-family ipv4

Specifies the IPv4 address family and enters address family configuration submode, and initializes the global address family.

Step 5

flowspec next-hop unchanged

Example:


RP/0/RP0/CPU0:router(config-bgp)# router bgp 100 neighbor 1.1.1.1 address-family ipv4 flowspec next-hop unchanged

Preserves the next-hop for the flowspec unchanged.

Validate BGP Flowspec

BGP Flowspec validation is enabled by default for flowspec SAFI routes for IPv4. VPN routes are not subject to the flow validation. A flow specification NLRI is validated to ensure that any one of the following conditions holds true for the functionality to work:

  • The originator of the flow specification matches the originator of the best-match unicast route for the destination prefix embedded in the flow specification.

  • There are no more specific unicast routes, when compared with the flow destination prefix, that have been received from a different neighboring AS than the best-match unicast route, which has been determined in the previous condition.

  • The AS_PATH and AS4_PATH attribute of the flow specification are empty.

  • The AS_PATH and AS4_PATH attribute of the flow specification does not contain AS_SET and AS_SEQUENCE segments.

Any path which does not meet these conditions, is appropriately marked by BGP and not installed in flowspec manager. Additionally, BGP enforces that the last AS added within the AS_PATH and AS4_PATH attribute of a EBGP learned flow specification NLRI must match the last AS added within the AS_PATH and AS4_PATH attribute of the best-match unicast route for the destination prefix embedded in the flow specification. Also, when the redirect-to-IP extended community is present, by default, BGP enforces the following check when receiving a flow-spec route from an eBGP peer:

If the flow-spec route has an IP next-hop X and includes a redirect-to-IP extended community, then the BGP speaker discards the redirect-to-ip extended community (and not propagate it further with the flow-spec route) if the last AS in the AS_PATH or AS4_PATH attribute of the longest prefix match for X does not match the AS of the eBGP peer.

Disable Flowspec Redirect and Validation explains the procedure to disable BGP flowspec validation.

Disabling BGP Flowspec

This procedure disables BGP flowspec policy on an interface.

SUMMARY STEPS

  1. configure
  2. interface type interface-path-id
  3. { ipv4 } flowspec disable
  4. Use the commit or end command.

DETAILED STEPS

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

interface type interface-path-id

Example:


RP/0/RP0/CPU0:router(config)# interface GigabitEthernet 0/1/1/1

Configures an interface and enters the interface configuration mode.

Step 3

{ ipv4 } flowspec disable

Example:


RP/0/RP0/CPU0:router(config-if)# ipv4 flowspec disable

Disable flowspec policy on the selected interface.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Disable flowspec on the interface

The following example shows you how you can disable BGP flowspec on an interface, and apply another PBR policy: 

Interface GigabitEthernet 0/0/0/0
 flowspec [ipv4] disable
int g0/0/0/1
service policy type pbr test_policy
 !
!

Disable Flowspec Redirect and Validation

You can disable flowspec validation as a whole for eBGP sessions by means of configuring an explicit knob.

SUMMARY STEPS

  1. configure
  2. router bgp as-number
  3. neighbor ip-address
  4. address-family { ipv4 }
  5. flowspec validation { disable | redirect disable }

DETAILED STEPS

  Command or Action Purpose

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config)# router bgp 100 neighbor 1.1.1.1

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

address-family { ipv4 }

Example:


RP/0/RP0/CPU0:router(config-bgp)# router bgp 100 neighbor 1.1.1.1 address-family ipv4

Specifies the IPv4 address family and enters address family configuration submode, and initializes the global address family.

Step 5

flowspec validation { disable | redirect disable }

Example:


RP/0/RP0/CPU0:router(config-bgp)# router bgp 100 neighbor 1.1.1.1 address-family ipv4 flowspec validation disable

You can choose to disable flowspec validation as a whole for all eBGP sessions or disable redirect nexthop validation.

Configuration Examples for Implementing BGP Flowspec

Flowspec Rule Configuration

Flowspec rule configuration example

In this example, two flowspec rules are created for two different VRFs with the goal that all packets to 10.0.1/24 from 192/8 and destination-port {range [137, 139] or 8080, rate limit to 500 bps in blue vrf and drop it in vrf-default. The goal is also to disable flowspec getting enabled on gig 0/0/0/0. 

class-map type traffic match-all fs_tuple

 match destination-address ipv4 10.0.1.0/24

 match source-address ipv4 192.0.0.0/8

 match destination-port 137-139 8080

 end-class-map

 !

!

policy-map type pbr fs_table_blue

 class type traffic fs_tuple

  police rate 500 bps

  !

 !

 class class-default

 !

 end-policy-map

policy-map type pbr fs_table_default

 class type traffic fs_tuple

  drop

  !

 !

 class class-default

 !

 end-policy-map

flowspec

 local-install interface-all

 address-family ipv4

  service-policy type pbr fs_table_default

  !

 !

 vrf blue

  address-family ipv4

   service-policy type pbr fs_table_blue local

   !

  !

 !

!

Interface GigabitEthernet 0/0/0/0

 vrf blue

 ipv4 flowspec disable

Drop Packet Length

This example shows a drop packet length action configuration: 
class-map type traffic match-all match-pkt-len
 match packet length 100-150
 end-class-map
!
policy-map type pbr test2
 class type traffic match-pkt-len
  drop
 !
 class type traffic class-default
 !
 end-policy-map
!

To configure a traffic class to discard packets belonging to a specific class, you use the drop command in policy-map class configuration mode. In this example, a multi-range packet length value from 100-150 has been defined. If the packet length of the incoming traffic matches this condition, the action is defined to 'drop' this packet.

Remark DSCP

This is an example of the set dscp action configuration. 

class-map type traffic match-all match-dscp-af11
 match dscp 10
 end-class-map
!
policy-map type pbr test6
 class type traffic match-dscp-af11
  set dscp af23
 !
 class type traffic class-default
 !
 end-policy-map
!

In this example, the traffic marking extended community (match dscp) instructs the system to modify or set the DSCP bits of a transiting IP packet from dscp 10 to dscp af23.

Additional References for BGP Flowspec

The following sections provide references related to implementing BGP Flowspec.

Related Documents

Related Topic

Document Title

BGP flowspec commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Routing Command Reference for Cisco NCS 6000 Series Routers

Standards

Standards

Title

draft-ietf-idr-flowspec-redirect-ip-01

draft-simpson-idr-flowspec-redirect-02

draft-ietf-idr-bgp-flowspec-oid-02

BGP Flow-Spec Redirect to IP Action

BGP Flow-Spec Extended Community for Traffic Redirect to IP Next Hop

Revised Validation Procedure for BGP Flow Specifications

RFCs

RFCs

Title

RFC 5575

Dissemination of Flow Specification Rules

Technical Assistance

Description

Link

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