OSPFv2 Cryptographic Authentication

To prevent unauthorized or invalid routing updates in your network, Open Shortest Path First version 2 (OSPFv2) protocol packets must be authenticated.

There are two methods of authentication that are defined for OSPFv2: plain text authentication and cryptographic authentication. This module describes how to configure cryptographic authentication using the Hashed Message Authentication Code - Secure Hash Algorithm (HMAC-SHA). OSPFv2 specification (RFC 2328) allows only the Message-Digest 5 (MD5) algorithm for cryptographic authentication. However, RFC 5709 (OSPFv2 HMAC-SHA Cryptographic Authentication) allows OSPFv2 to use HMAC-SHA algorithms for cryptographic authentication.

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Prerequisites for OSPFv2 Cryptographic Authentication

Ensure that Open Shortest Path First version 2 (OSPFv2) is configured on your network.

Information About OSPFv2 Cryptographic Authentication

Configuring OSPFv2 Cryptographic Authentication

The OSPFv2 Cryptographic Authentication feature allows you to configure a key chain on the OSPF interface to authenticate OSPFv2 packets by using HMAC-SHA algorithms. You can use an existing key chain that is being used by another protocol, or you can create a key chain specifically for OSPFv2.

A key chain is a list of keys. Each key consists of a key string, which is also called the password or passcode. A key-string is essential for a key to be operational. Each key is identified by a unique key ID. To authenticate the OSPFv2 packets, it is essential that the cryptographic authentication algorithm be configured with a key. OSPFv2 supports keys with key IDs ranging from 1 to 255. The combination of the cryptographic authentication algorithm and the key is known as a Security Association (SA).

The authentication key on a key chain is valid for a specific time period called lifetime. An SA has the following configurable lifetimes:

  • Accept lifetime

  • Send lifetime

While adding a new key, the Send lifetime is set to a time in the future so that the same key can be configured on all devices in the network before the new key becomes operational. Old keys are removed only after the new key is operational on all devices in the network. When packets are received, the key ID is used to fetch the data for that key. The packet is verified using the cryptographic authentication algorithm and the configured key ID. If the key ID is not found, the packet is dropped.


Note

When key chain has more than one key, OSPF selects the key that has the maximum life time. Key having an infinite lifetime is preferred. If keys have the same lifetime, then key with the higher key ID is preferred.

Use the ip ospf authentication key-chain command to configure key chains for OSPFv2 cryptographic authentication.


Note

If OSPFv2 is configured to use a key chain, all MD5 keys that were previously configured using the ip ospf message-digest-key command are ignored.

How to Configure OSPFv2 Cryptographic Authentication

Defining a Key Chain

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. key chain name
  4. key key-id
  5. key-string name
  6. cryptographic-algorithm name
  7. send-lifetime start-time { infinite | end-time | duration seconds }
  8. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

key chain name

Example:


Device(config)# key chain sample1

Specifies the key chain name and enters key-chain configuration mode.

Step 4

key key-id

Example:


Device(config-keychain)# key 1

Specifies the key identifier and enters key-chain key configuration mode. The range is from 1 to 255.

Step 5

key-string name

Example:


Device(config-keychain-key)# key-string string1

Specifies the key string.
Step 6

cryptographic-algorithm name

Example:


Device(config-keychain-key)# cryptographic-algorithm hmac-sha-256

Configures the key with the specified cryptographic algorithm.
Step 7

send-lifetime start-time { infinite | end-time | duration seconds }

Example:


Device(config-keychain-key)# send-lifetime local 10:00:00 5 July 2013 infinite

Sets the time period during which an authentication key on a key chain is valid to be sent during key exchange with another device.

Step 8

end

Example:


Device(config-keychain-key)# end

Exits key-chain key configuration mode and returns to privileged EXEC mode.

Defining Authentication on an Interface

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ip ospf authentication key-chain name
  5. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:


Device(config)# interface gigabitethernet0/0/0

Specifies an interface type and number and enters interface configuration mode.

Step 4

ip ospf authentication key-chain name

Example:


Device(config-if)# ip ospf authentication key-chain ospf1

Specifies the key chain for an interface.

Step 5

end

Example:


Device(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Configuration Examples for OSPFv2 Cryptographic Authentication

Example: Defining a Key Chain

The following example shows how to configure a key chain:

Device> enable
Device# configure terminal
Device(config)# key chain sample1
Device(config-keychain)# key 1
Device(config-keychain-key)# key-string ThisIsASampleKey12345 
Device(config-keychain-key)# cryptographic-algorithm hmac-sha-256 
Device(config-keychain-key)# send-lifetime local 10:00:00 5 July 2013 infinite
Device(config-keychain-key)# end

Example: Verifying a Key Chain

The following sample output from the show key chain command displays the key chain information: 

Device# show key chain Key-chain sample1

     key 1 -- text "ThisIsASampleKey12345"
         accept lifetime (always valid) - (always valid) [valid now]
         send lifetime (10:00:00 PDT Jul 5 2013) - (infinite)

The table below describes the significant fields in the output:

Table 1. show ip ospf interface Field Descriptions

Field

Description

key

Status of the configured key.

accept lifetime

The time interval within which the device accepts the key during key exchange with another device.

send lifetime

The time interval within which the device sends the key during a key exchange with another device.

Example: Defining Authentication on an Interface

The following example shows how to define authentication on Gigabit Ethernet interface 0/0/0:

Device> enable
Device# configure terminal
Device(config)# interface GigabitEthernet0/0/0
Device (config-if)# ip ospf authentication key-chain sample1
Device (config-if)# end

Example: Verifying Authentication on an Interface

The following sample output of the show ip ospf interface command displays the cryptographic key information: 

Device# show ip ospf interface GigabitEthernet0/0/0 

GigabitEthernet0/0/0 is up, line protocol is up 
  Internet Address 192.168.8.2/24, Area 1, Attached via Interface Enable
  Process ID 1, Router ID 10.1.1.8, Network Type BROADCAST, Cost: 10
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           10        no          no            Base
  Enabled by interface config, including secondary ip addresses
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 10.1.1.8, Interface address 192.168.8.2
  Backup Designated router (ID) 10.1.1.9, Interface address 192.168.8.9
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:00
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Can be protected by per-prefix Loop-Free FastReroute
  Can be used for per-prefix Loop-Free FastReroute repair paths
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 10.1.1.9  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)
  Cryptographic authentication enabled
    Sending SA: Key 25, Algorithm HMAC-SHA-256 – key chain sample1

The table below describes the significant fields in the output:

Table 2. show ip ospf interface Field Descriptions

Field

Description

GigabitEthernet

Status of the physical link and operational status of the protocol.

Internet Address

Interface IP address, subnet mask, and area address.

Area

OSPF area.

Process ID

OSPF process ID.

Cost

Administrative cost assigned to the interface.

Topology-MTID

MTR topology Multitopology Identifier (MTID) is a number assigned so that the protocol can identify the topology associated with information that it sends to its peers.

Transmit Delay

Transmit delay (in seconds), interface state, and router priority.

State

Operational state of the interface.

Designated Router

Designated router ID and respective interface IP address.

Backup Designated router

Backup designated router ID and respective interface IP address.

Timer intervals configured

Configuration of timer intervals.

Neighbor Count

Count of network neighbors and list of adjacent neighbors.

Cryptographic authentication

Status of cryptographic authentication.

Sending SA

Status of the sending SA (Security Association). Key, cryptographic algorithm, and key chain used.

Additional References for OSPFv2 Cryptographic Authentication

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

OSPF commands

Cisco IOS IP Routing: OSPF Command Reference

Standards and RFCs

Standard

Title

RFC 2328

OSPF Version 2, April 1998

RFC 5709

OSPFv2 HMAC-SHA Cryptographic Authentication, October 2009

Technical Assistance

Description

Link

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http://www.cisco.com/cisco/web/support/index.html

Feature Information for OSPFv2 Cryptographic Authentication

Table 3. Feature Information for OSPFv2 Cryptographic Authentication

Feature Name

Releases

Feature Information

OSPFv2 Cryptographic Authentication

15.4(1)T

The OSPFv2 Cryptographic Authentication feature prevents unauthorized or invalid routing updates in your network by authenticating Open Shortest Path First version 2 (OSPFv2) protocol packets using HMAC-SHA algorithms.

The following command was modified: ip ospf authentication.