IPv6 eBGP and iBGP

IPv6 iBGP: The Internal Fabric

In an iBGP setup, the goal is to ensure all routers within your organization know how to reach external destinations.

• The Full Mesh Requirement: Since iBGP routers do not re-advertise prefixes learned from one iBGP peer to another (to pr+event loops), you typically need a "Full Mesh" or Route Reflectors.
• Next-Hop-Self: Because iBGP doesn't change the next-hop attribute, internal routers often don't know how to reach the original eBGP exit point. Using the next-hop-self command is a standard practice to ensure internal reachability.

IPv6 eBGP: Crossing the Border

eBGP is the handshake between different entities (like your network and an ISP).

• Prefix Filtering: Unlike iBGP, you never trust an eBGP peer blindly. Strict prefix-lists and route-maps are essential to ensure you aren't leaking private routes or accepting "bogon" space.
• The Link-Local Trap: In IPv6, eBGP can technically peer using Link-Local addresses (fe80::/10), but for stability and clarity, most engineers stick to Global Unicast Addresses (GUA) for peering.

In this blog, we configure the basics of IPv6 eBGP and iBGP. 

Topology:

• Configure the topology as per the diagram.
• Configure the IPv6 addresses as per the topology.
• Configure IBGP on router 1 and router 2.
• Advertise directly connected.
• Configure EBGP on router 3
• Configure next-hop-self on router 2 for router 1
• Verify the configuration with ping, traceroute and show commands.

R1(config)#interface fastethernet 0/0
R1(config-if)#ipv6 address 2001:12::1/64
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#interface loopback 1
R1(config-if)#ipv6 address fc00:11::1/64
R1(config-if)#no shutdown
R1(config-if)#exit

R2(config)#interface fastethernet 0/0

R2(config-if)#ipv6 address 2001:12::2/64

R2(config-if)#no shutdown

R2(config-if)#exit

R2(config)#interface loopback 1

R2(config-if)#ipv6 address fc00:22::1/64

R2(config-if)#no shutdown

R2(config-if)#exit

R2(config)#interface serial 2/0

R2(config-if)#ipv6 address 2001:23::1/64

R2(config-if)#no shutdown

R2(config-if)#exit

R3(config)#interface loopback 1

R3(config-if)#ipv6 address fc00:33::1/64

R3(config-if)#no shutdown

R3(config-if)#exit

R3(config)#interface serial 2/0

R3(config-if)#ipv6 address 2001:23::2/64

R3(config-if)#no shutdown

R3(config-if)#exit

R1(config)#ipv6 unicast-routing

R1(config)#router bgp 6500

R1(config-router)#bgp router-id 1.1.1.1

R1(config-router)#no bgp default ipv4-unicast

R1(config-router)#neighbor 2001:12::2 remote-as 6500

R1(config-router)#address-family ipv6 unicast

R1(config-router-af)#neighbor 2001:12::2 activate

R1(config-router-af)#network fc00:11::/64

R1(config-router-af)#network 2001:12::/64

R1(config-router-af)#exit

R2(config)#ipv6 unicast-routing

R2(config)#router bgp 6500

R2(config-router)#bgp router-id 2.2.2.2

R2(config-router)#no bgp default ipv4-unicast

R2(config-router)#neighbor 2001:12::1 remote-as 6500

R2(config-router)#neighbor 2001:23::2 remote-as 6700

R2(config-router)#address-family ipv6 unicast

R2(config-router-af)#neighbor 2001:12::1 activate

R2(config-router-af)#neighbor 2001:23::2 activate

R2(config-router-af)#network fc00:22::/64

R2(config-router-af)#network 2001:12::/64

R2(config-router-af)#network 2001:23::/64

R2(config-router-af)#exit

%BGP-5-ADJCHANGE: neighbor 2001:12::1 Up

R2(config)#router bgp 6500

R2(config-router)#address-family ipv6 unicast

R2(config-router-af)#neighbor 2001:12::1 next-hop-self

R2(config-router-af)#exit

R3(config)#ipv6 unicast-routing

R3(config)#router bgp 6700

R3(config-router)#bgp router-id 3.3.3.3

R3(config-router)#no bgp default ipv4-unicast

R3(config-router)#neighbor 2001:23::1 remote-as 6500

R3(config-router)#address-family ipv6 unicast

R3(config-router-af)#neighbor 2001:23::1 activate

R3(config-router-af)#network fc00:33::/64

R3(config-router-af)#network 2001:23::/64

R3(config-router-af)#exit

%BGP-5-ADJCHANGE: neighbor 2001:23::1 Up

R1#show ip bgp ipv6 unicast summary

BGP router identifier 1.1.1.1, local AS number 6500

BGP table version is 7, main routing table version 7

5 network entries using 860 bytes of memory

6 path entries using 528 bytes of memory

3/3 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1820 total bytes of memory

BGP activity 7/2 prefixes, 8/2 paths, scan interval 60 secs

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

2001:12::2      4         6500      24      21        7    0    0 00:16:06        4

R1#show ipv6 route bgp

IPv6 Routing Table - default - 8 entries

Codes: C - Connected, L - Local, S - Static, U - Per-user Static route

       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP

       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea

       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO

       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect

       O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP

B   2001:23::/64 [200/0]

     via 2001:12::2

B   FC00:22::/64 [200/0]

     via 2001:12::2

B   FC00:33::/64 [200/0]

     via 2001:12::2

R2#ping fc00:11::1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to FC00:11::1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 24/30/40 ms

R2#ping fc00:33::1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to FC00:33::1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/28/36 ms

R1#traceroute fc00:33::1

Type escape sequence to abort.

Tracing the route to FC00:33::1

  1 2001:12::2 20 msec 28 msec 20 msec

  2 2001:23::2 44 msec 64 msec 40 msec

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