Dell SmartFabric OS10 User Guide Release 10.5.3

BGP over unnumbered interfaces

As BGP relies on TCP for connection between peers, the interface that connects to the peer requires a unique IP address.

Assigning an IP address to every interface may exhaust the available pool of IP addresses and is error prone. Unnumbered interfaces are the interfaces without unique IP addresses. BGP unnumbered interfaces use the extended Next Hop encoding (ENHE) feature, which is defined by RFC 5549. BGP unnumbered interfaces advertise IPv4 routes with an IPv6 Next Hop.

As IPv6 link-local addresses automatically configure on connected interfaces, BGP uses these link-local addresses to form neighborship. Unnumbered interfaces use IPv6 router advertisements to identify the address of the peer.

Restrictions

• You cannot configure VRRP for IPv6 on an unnumbered interface. This configuration causes BGP session failure.
• You cannot use the default VLAN as the unnumbered VLAN.
• Route reflectors are not supported with unnumbered peers.
• Confederations are not supported with unnumbered peers.
• Dampening is not supported with unnumbered peers.

Configure an unnumbered neighbor

1. Create an interface, if required, in CONFIGURATION mode.

   interface interface-type

   interface interface-type—(Optional) Enter one of the following interface types:
   • ethernet node/slot/port[:subport]—Display Ethernet interface information.
   • port-channel id-number—Display port channel interface IDs, from 1 to 999 or 1001 to 2000.
   • vlan vlan-id—Display the VLAN interface number, from 1 to 4093.
2. Enable RAs on the interface in INTERFACE mode.

   ipv6 nd send-ra

3. Configure minimum and maximum RA intervals in INTERFACE mode.

   ipv6 nd min-ra-interval 3
   ipv6 nd max-ra-interval 4

4. Enable BGP on the device.

   router bgp as-number

5. Enter an unnumbered neighbor in ROUTER-BGP mode.

   neighbor interface interface-type

   interface interface-type—(Optional) Enter one of the following interface types:
   • ethernet node/slot/port[:subport]—Display Ethernet interface information.
   • port-channel id-number—Display port channel interface IDs, from 1 to 999 or 1001 to 2000.
   • vlan vlan-id—Display the VLAN interface number, from 1 to 4093.
6. Enable the BGP neighbor in ROUTER-NEIGHBOR mode.

   no shutdown

Example for configuring an unnumbered neighbor

OS10(config)# interface ethernet 1/1/1
OS10(conf-if-eth1/1/1)# ipv6 nd max-ra-interval 4
OS10(conf-if-eth1/1/1)# ipv6 nd min-ra-interval 3
OS10(conf-if-eth1/1/1)# ipv6 nd send-ra
OS10(conf-if-eth1/1/1)# no shutdown
OS10(conf-if-eth1/1/1)# exit
OS10(config)# router bgp 100
OS10(config-router-bgp-100)# neighbor interface ethernet 1/1/1
OS10(config-router-neighbor)# no shutdown

Example outputs for viewing unnumbered BGP interfaces

OS10# show ip bgp
BGP local RIB : Routes to be Added , Replaced , Withdrawn
BGP local router ID is 14.233.209.106
Status codes: s suppressed, S stale, d dampened, h history, * valid, > best
Path source: I - internal, a - aggregate, c - confed-external,
r - redistributed/network, S - stale
Origin codes: i - IGP, e - EGP, ? - incomplete
       Network        Next Hop         Metric   LocPrf    Weight   Path
*>r    31.1.1.0/24    0.0.0.0            0        100     32768     ?

*>     41.1.1.0/24    ethernet 1/1/1     0        100     32768     ?

OS10# show ip bgp neighbors interface ethernet1/1/1

BGP neighbor is fe80::76e6:e2ff:fef6:b81 via ethernet1/1/1, remote AS 100, local AS 200  external link
  BGP version 4, remote router ID 125.12.57.117
  BGP state ESTABLISHED, in this state for 00:15:52
  Last read 00:21:08 seconds
  Hold time is 180, keepalive interval is 60 seconds
  Configured hold time is 180, keepalive interval is 60 seconds
  Fall-over disabled

  Received 20 messages
    1 opens, 0 notifications, 0 updates
    19 keepalives, 0 route refresh requests
  Sent 20 messages
    1 opens, 1 notifications, 0 updates
    18 keepalives, 0 route refresh requests
  Minimum time between advertisement runs is 30 seconds
  Minimum time before advertisements start is  0 seconds

  Capabilities received from neighbor for IPv4 Unicast:
   MULTIPROTO_EXT(1)
    ROUTE_REFRESH(2)
    CISCO_ROUTE_REFRESH(128)
    4_OCTET_AS(65)
    Extended Next Hop Encoding (5)
Capabilities advertised to neighbor for IPv4 Unicast:
    MULTIPROTO_EXT(1)
    ROUTE_REFRESH(2)
    CISCO_ROUTE_REFRESH(128)
    4_OCTET_AS(65)
    Extended Next Hop Encoding (5)
Prefixes accepted 0, Prefixes advertised 0
  Connections established 1; dropped 0
  Last reset never
   Prefixes ignored due to:
    Martian address  0, Our own AS in AS-PATH 0
    Invalid Nexthop  0, Invalid AS-PATH length 0
    Wellknown community 0, Locally originated 0

Local host: fe80::76e6:e2ff:fef5:b281, Local port: 45926
Foreign host: fe80::76e6:e2ff:fef6:b81, Foreign port: 179