To view the details of the IPv4 or IPv6 CEF tables, use the following commands:

• show cef {ipv4 address | ipv6 address} hardware egress

Displays the IPv4 or IPv6 CEF table. The next hop and forwarding interface are displayed for each prefix. The output of the show cef command varies by location.

Router# show cef 203.0.1.2 hardware egress 
  203.0.1.2/32, version 0, internal 0x1020001 0x0 (ptr 0x8d7db7f0) [1], 0x0 (0x8daeedf0), 0x0 (0x0)
 Updated Nov 20 13:33:23.557
 local adjacency 203.0.1.2
 Prefix Len 32, traffic index 0, Adjacency-prefix, precedence n/a, priority 15
   via 203.0.1.2/32, HundredGigE0/0/1/0, 3 dependencies, weight 0, class 0 [flags 0x0]
    path-idx 0 NHID 0x0 [0x8cfc81a0 0x0]
    next hop 203.0.1.2/32
    local adjacency

• show cef {ipv4 | ipv6} summary

Router#show cef ipv4 summary
Fri Nov 20 13:50:45.239 UTC

Router ID is 216.1.1.1

IP CEF with switching (Table Version 0) for node0_RP0_CPU0

  Load balancing: L4
  Tableid 0xe0000000 (0x8cf5b368), Vrfid 0x60000000, Vrid 0x20000000, Flags 0x1019
  Vrfname default, Refcount 4129
  56 routes, 0 protected, 0 reresolve, 0 unresolved (0 old, 0 new), 7616 bytes
  13 rib, 0 lsd, 0:27 aib, 1 internal, 10 interface, 4 special, 1 default routes
  56 load sharing elements, 24304 bytes, 1 references
  1 shared load sharing elements, 432 bytes
  55 exclusive load sharing elements, 23872 bytes
  0 route delete cache elements
  13 local route bufs received, 1 remote route bufs received,  0 mix bufs received
  13 local routes, 0 remote routes
  13 total local route updates processed
  0 total remote route updates processed
  0 pkts pre-routed to cust card
  0 pkts pre-routed to rp card
  0 pkts received from core card
  0 CEF route update drops, 0 revisions of existing leaves
  0 CEF route update drops due to version mis-match
  Resolution Timer: 15s
  0 prefixes modified in place
  0 deleted stale prefixes
  0 prefixes with label imposition, 0 prefixes with label information
  0 LISP EID prefixes, 0 merged, via 0 rlocs
 28 next hops
  1 incomplete next hop

 0 PD backwalks on LDIs with backup path

• show cef { ipv4 address | ipv6 address } detail

Displays the details of the IPv4 or IPv6 CEF table.

Router#show cef 203.0.1.2 detail 
203.0.1.2/32, version 0, internal 0x1020001 0x0 (ptr 0x8d7db7f0) [1], 0x0 (0x8daeedf0), 0x0 (0x0)
 Updated Nov 20 13:33:23.556
 local adjacency 203.0.1.2
 Prefix Len 32, traffic index 0, Adjacency-prefix, precedence n/a, priority 15
  gateway array (0x8d84beb0) reference count 1, flags 0x0, source aib (10), 0 backups
                [2 type 3 flags 0x8401 (0x8d99a598) ext 0x0 (0x0)]
  LW-LDI[type=3, refc=1, ptr=0x8daeedf0, sh-ldi=0x8d99a598]
  gateway array update type-time 1 Nov 20 13:33:23.556
 LDI Update time Nov 20 13:33:23.556
 LW-LDI-TS Nov 20 13:33:23.556
   via 203.0.1.2/32, HundredGigE0/0/1/0, 3 dependencies, weight 0, class 0 [flags 0x0]
    path-idx 0 NHID 0x0 [0x8cfc81a0 0x0]
    next hop 203.0.1.2/32
    local adjacency
        Load distribution: 0 (refcount 2)

    Hash  OK  Interface                 Address
    0     Y   HundredGigE0/0/1/0        203.0.1.2
    

• show adjacency detail

Displays detailed adjacency information, including Layer 2 information for each interface. The output of the show adjacency command varies by location.

Router#show adjacency detail

-------------------------------------------------------------------------------
0/5/CPU0
-------------------------------------------------------------------------------
Interface                   Address                  Version  Refcount Protocol
Hu0/5/0/12                  (interface)                   13        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/30                  (interface)                   31        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/19                  (interface)                   20        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/16                  (interface)                   17        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/23                  (interface)                   24        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/22                  (interface)                   23        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/1                   (interface)                    2        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/6                   (interface)                    7        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/10                  (interface)                   11        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/31                  (interface)                   32        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/28                  (interface)                   29        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/35                  (interface)                   36        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/32                  (interface)                   33        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/15                  (interface)                   16        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/34                  (interface)                   35        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/2                   (interface)                    3        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/26                  (interface)                   27        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/0/0/9                   203.0.1.2                     50        2(    0) mpls
                           00109400000cea285f0b80248847
                           mtu: 8986, flags 1 0


Hu0/0/0/9                   203.0.1.2                     49        2(    0) ipv4
                           00109400000cea285f0b80240800
                           mtu: 8986, flags 1 0


Hu0/5/0/29                  (interface)                   30        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/33                  (interface)                   34        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/20                  (interface)                   21        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/24                  (interface)                   25        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/0                   (interface)                    1        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/4                   (interface)                    5        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/8                   (interface)                    9        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/3                   (interface)                    4        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/27                  (interface)                   28        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/7                   (interface)                    8        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/14                  (interface)                   15        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/11                  (interface)                   12        1(    0)
                           (interface entry)
                           mtu: 1500, flags 1 4


Hu0/5/0/18                  (interface)                   19        1(    0)
                           (interface entry)

The system inherently supports the 7-tuple hash algorithm. Load balancing describes the functionality in a router that distributes packets across multiple links based on Layer 3 (network layer) and Layer 4 (transport layer) routing information. If the router discovers multiple paths to a destination, the routing table is updated with multiple entries for that destination.

Per-flow load balancing performs these functions:

• Incoming data traffic is evenly distributed over multiple equal-cost connections.

• Incoming data traffic is evenly distributed over multiple equal-cost connections member links within a bundle interface.

• Layer 2 bundle and Layer 3 (network layer) load balancing decisions are taken on IPv4, IPv6, and MPLS flows . If it is an IPv4 or an IPv6 payload, then a 7-tuple hashing is done. If it is an MPLS payload with three or less labels, then the hardware parses the payload underneath and identifies whether the payload packet has an IPv4 or an IPv6 header. If it is an IPv4 or IPv6 header, then a 4-tuple hashing is performed based on the IP source, IP destination, router ID, and label stack; otherwise, an MPLS label based hashing is performed. In case of MPLS label-based hashing, the top 4 labels are used in hash computation..

• A 7-tuple hash algorithm provides more granular load balancing and used for load balancing over multiple equal-cost Layer 3 (network layer) paths. The Layer 3 (network layer) path is on a physical interface or on a bundle interface. In addition, load balancing over member links can occur within a Layer 2 bundle interface.

• The 7-tuple load-balance hash calculation contains:

  • Source IP address

  • Destination IP address

  • IP Protocol type

  • Router ID

  • Source port

  • Destination port

  • Input interface

Load balancing decisions are taken based on a packet header, type of load balancing, type of scenario and platform specifics as follows:

• Packet header can contain one or many MAC, MPLS, IPv4 or IPv6 address, TCPor UDP headers, and so on.

• Load balancing can be done during ECMP or LAG (Bundle-Ether) forwarding.

• Scenarios can include IP forwarding, IP tunnel forwarding or decapsulation, MPLS forwarding or disaggregation, or Ethernet forwarding.

• The chipset type contains a packet’s fields. These fields are considered for load balancing.

The following tables includes detailed list of options, list of scenarios, and headers fields to specify how ECMP or LAG load balancing is done.

Note:

• Only the fields that are highlighted in bold font are used for load balancing hash calculations. For example, for IP forwarding for IPv4 or IPv6 header and L4 (TCP or UDP) header, ECMP or LAG load balancing is done based on:

  • Source and destination IPv4 or IPv6 addresses

  • L4 source and destination ports

• To modify the hashing algorithm that is used for ECMP and bundle member selection, use the hw-module profile load-balance algorithm command in XR Config mode.

Note	For MPLS packets, up to four labels are used for hash calculation.

Note	For MPLS packets, up to four labels are used for hash calculation.

Note	For MPLS packets with multiple labels, hash calculation is done based on the first five labels along other headers.

Note	For MPLS packets with one through three labels, only the first label is used for load balancing along with other headers.

Note	For MPLS packets with multiple labels, hash calculation is done based on first five labels along with other headers.

Routers forward packets using either route information from route table entries that you manually configure or the route information that is calculated using dynamic routing algorithms. Static routes, which define explicit paths between two routers, cannot be automatically updated; you must manually reconfigure static routes when network changes occur. Static routes use less bandwidth than dynamic routes. Use static routes where network traffic is predictable and where the network design is simple. You should not use static routes in large, constantly changing networks because static routes cannot react to network changes. Most networks use dynamic routes to communicate between routers but might have one or two static routes configured for special cases. Static routes are also useful for specifying a gateway of last resort (a default router to which all unroutable packets are sent).

Configuration Example

Create a static route between Router A and B over a HundredGigE interface. The destination IP address is 203.0.1.2/32 and the next hop address is 1.0.0.2.

Router(config)#router static address-family ipv4 unicast 
Router(config-static-afi)#203.0.1.2/32 HundredGigE 0/0/1/1 1.0.0.2
Router(config-static-afi)#commit

Router#show running-config router static address-family ipv4 unicast
router static
 address-family ipv4 unicast
 203.0.1.2/32 HundredGigE 0/0/1/1 1.0.0.2
 !
!

Router#show cef 203.0.1.2/32 hardware egress details location 0/0/CPU0
Wed Nov  6 10:09:23.548 UTC
111.0.0.1/32, version 221, attached, internal 0x1000041 0x0 (ptr 0x8b00ea80) [1], 0x0 (0x8afd9768), 0x0 (0x0)
Updated Nov  6 10:08:07.424
Prefix Len 32, traffic index 0, precedence n/a, priority 2
  gateway array (0x8ae4baf0) reference count 1, flags 0x0, source rib (7), 0 backups
                [2 type 3 flags 0x40008441 (0x8af020c0) ext 0x0 (0x0)]
  LW-LDI[type=3, refc=1, ptr=0x8afd9768, sh-ldi=0x8af020c0]
  gateway array update type-time 1 Nov  6 10:08:07.423
LDI Update time Nov  6 10:08:07.423
LW-LDI-TS Nov  6 10:08:07.424
   via tunnel-ip1, 0 dependencies, recursive [flags 0x8]
    path-idx 0 NHID 0x0 [0x8ae0d728 0x0]
    local adjacency
 
 

The BGP Attributes Download feature enables you to display the installed BGP attributes in CEF.

• The show cef bgp-attribute command displays the installed BGP attributes in CEF.

• The show cef bgp-attribute attribute-id command and the show cef bgp-attribute local-attribute-id command are used to view the specific BGP attributes by attribute ID and local attribute ID.

Router# show cef bgp-attribute
Router ID is 216.1.1.1

IP CEF with switching (Table Version 0) for node0_RP0_CPU0

  Load balancing: L4
  Tableid 0xe0000000 (0x8cf5b368), Vrfid 0x60000000, Vrid 0x20000000, Flags 0x1019
  Vrfname default, Refcount 4129
  56 routes, 0 protected, 0 reresolve, 0 unresolved (0 old, 0 new), 7616 bytes
  13 rib, 0 lsd, 0:27 aib, 1 internal, 10 interface, 4 special, 1 default routes
  56 load sharing elements, 24304 bytes, 1 references
  1 shared load sharing elements, 432 bytes
  55 exclusive load sharing elements, 23872 bytes
  0 route delete cache elements
  13 local route bufs received, 1 remote route bufs received,  0 mix bufs received
  13 local routes, 0 remote routes
  13 total local route updates processed
  0 total remote route updates processed
  0 pkts pre-routed to cust card
  0 pkts pre-routed to rp card
  0 pkts received from core card
  0 CEF route update drops, 0 revisions of existing leaves
  0 CEF route update drops due to version mis-match
  Resolution Timer: 15s
  0 prefixes modified in place
  0 deleted stale prefixes
  0 prefixes with label imposition, 0 prefixes with label information
  0 LISP EID prefixes, 0 merged, via 0 rlocs
 28 next hops
  1 incomplete next hop

 0 PD backwalks on LDIs with backup path


VRF: default
_____________
Table ID: 0xe0000000. Total number of entries: 0
OOR state: GREEN. Number of OOR attributes: 0

When CEF installs a route for which there is no layer 2 adjacency information, CEF creates an incomplete layer 3 next-hop and programs it on the hardware. Because of this incomplete programming, the first packet will be forwarded to the software forwarding path. The software forwarding in turn strips off the layer 2 header from the packet and forwards it to ARP (Address Resolution Protocol) or ND (Neighbor Discovery) in order to resolve the layer 2 adjacency information. In such a packet, if there is feature specific information present in the layer 2 header, the software forwarding path fails to strip off the layer 2 header completely and thus ARP or ND is unable to resolve the missing layer 2 adjacency information and thereby this results in traffic being dropped.

Proactive ARP and ND feature solves the above problem by ensuring that CEF proactively triggers ARP or ND in order to resolve the missing layer 2 adjacency information, retrying every 15 seconds until the next-hop information is resolved. Thus, when you configure a static route which has an incomplete next-hop information, this feature automatically triggers ARP or ND resolution.

/* Enter the configuration mode and configure Proactive ARP/ND */
Router# configure
Router(config)# cef proactive-arp-nd enable
Router(config)# commit

Show running-config
cef proactive-arp-nd enable
end

PPPoE provides a standard method of employing the authentication methods of the Point-to-Point Protocol (PPP) over an Ethernet network. When used by Internet Service Providers (ISPs), PPPoE allows authenticated assignment of IP addresses. In this type of implementation, the PPPoE client and server are interconnected by Layer 2 bridging protocols that run over a DSL or other broadband connection.

PPPoE has two phases:

• Active Discovery Phase - In this phase, the PPPoE client locates a PPPoE server, called an access concentrator. During this phase, the system assigns a session ID and then, a PPPoE layer is established.

• PPP Session Phase - In this phase, the system negotiates PPP options and performs authentication on IP addresses. Once the link setup is complete, PPPoE functions as a Layer 2 encapsulation method, which allows data transfer over the PPP link within PPPoE headers.