IPv6 - BGP MED
Lab:
Disclaimer
This Configuration Guide is designed to assist members to enhance their skills in particular technology area. While every effort has been made to ensure that all material is as complete and accurate as possible, the enclosed material is presented on an “as is” basis. Neither the authors nor Forum assume any liability or responsibility to any person or entity with respect to loss or damages incurred from the information contained in this guide. This configuration guide was developed by Forum. Any similarities between material presented in this configuration guide and any other material is completely coincidental.
Cisco IOS Software, 7200 Software (C7200-ADVENTERPRISEK9-M), Version 15.0(1)M9, RELEASE SOFTWARE (fc1)
R1 Router Config:
!
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
no ip address
ipv6 address 2002:0:1:1::1/128
ipv6 ospf 1 area 0
!
interface Loopback1
no ip address
ipv6 address 2002:0:1:2::1/128
ipv6 ospf 1 area 0
!
interface Loopback2
no ip address
ipv6 address 2002:0:1:3::1/128
ipv6 ospf 1 area 0
!
interface Serial1/0
no ip address
ipv6 address 2001:0:0:12::1/128
ipv6 ospf 1 area 0
no fair-queue
serial restart-delay 0
!
interface Serial1/1
ipv6 address 2001:0:0:13::1/64
serial restart-delay 0
!
router bgp 65100
bgp router-id 1.1.1.1
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2001:0:0:13::3 remote-as 65000
neighbor 2002:0:2:1::2 remote-as 65000
neighbor 2002:0:2:1::2 ebgp-multihop 5
neighbor 2002:0:2:1::2 update-source
Loopback0
!
address-family ipv6
no synchronization
network 2002:0:1:2::1/128
network 2002:0:1:3::1/128
neighbor 2001:0:0:13::3 activate
neighbor 2002:0:2:1::2 activate
exit-address-family
!
ipv6 router ospf 1
router-id 1.1.1.1
log-adjacency-changes
!
R4 Router Config:
!
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
no ip address
ipv6 address 2002:0:4:1::4/128
!
interface Loopback1
no ip address
ipv6 address 2002:0:4:2::4/128
!
interface Loopback2
no ip address
ipv6 address 2002:0:4:3::4/128
!
interface Serial1/0
no ip address
ipv6 address 2001:0:0:34::4/128
serial restart-delay 0
clock rate 64000
!
router bgp 65200
bgp router-id 4.4.4.4
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2002:0:3:1::3 remote-as 65000
neighbor 2002:0:3:1::3 ebgp-multihop 5
neighbor 2002:0:3:1::3 update-source
Loopback0
!
address-family ipv6
no synchronization
network 2002:0:4:2::4/128
network 2002:0:4:3::4/128
neighbor 2002:0:3:1::3 activate
exit-address-family
!
ipv6 route 2001:0:0:34::3/128 Serial1/0
ipv6 route 2002:0:3:1::3/128 Serial1/0
!
R2 Router Config:
!
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
no ip address
ipv6 address 2002:0:2:1::2/128
ipv6 ospf 1 area 0
!
interface Loopback1
no ip address
ipv6 address 2002:0:2:2::2/128
ipv6 ospf 1 area 0
!
interface Loopback2
no ip address
ipv6 address 2002:0:2:3::2/128
ipv6 ospf 1 area 0
!
interface Serial1/0
no ip address
ipv6 address 2001:0:0:12::/64 eui-64
ipv6 ospf 1 area 0
no fair-queue
serial restart-delay 0
clock rate 64000
!
interface FastEthernet2/0
no ip address
duplex full
speed 100
ipv6 address 2001:0:0:23::/64 eui-64
ipv6 ospf 1 area 0
!
router bgp 65000
bgp router-id 2.2.2.2
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2001::23:C803:CFF:FE78:38
remote-as 65000
neighbor 2002:0:1:1::1 remote-as 65100
neighbor 2002:0:1:1::1 ebgp-multihop 5
neighbor 2002:0:1:1::1 update-source
Loopback0
!
address-family ipv6
no synchronization
network 2002:0:2:2::2/128
network 2002:0:2:3::2/128
neighbor 2001::23:C803:CFF:FE78:38
activate
neighbor 2002:0:1:1::1 activate
exit-address-family
!
ipv6 router ospf 1
router-id 2.2.2.2
log-adjacency-changes
!
R3 Router Config:
!
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
no ip address
ipv6 address 2002:0:3:1::3/128
ipv6 ospf 1 area 0
!
interface Loopback1
no ip address
ipv6 address 2002:0:3:2::3/128
ipv6 ospf 1 area 0
!
interface Loopback2
no ip address
ipv6 address 2002:0:3:3::3/128
ipv6 ospf 1 area 0
!
interface Serial1/0
no ip address
ipv6 address 2001:0:0:34::3/128
no fair-queue
serial restart-delay 0
clock rate 64000
!
interface Serial1/1
no ip address
ipv6 address 2001:0:0:13::3/64
serial restart-delay 0
!
interface FastEthernet2/0
mac-address ca03.0c78.0038
no ip address
duplex auto
speed auto
ipv6 address 2001:0:0:23::/64 eui-64
ipv6 ospf 1 area 0
!
router bgp 65000
bgp router-id 3.3.3.3
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2001:0:0:13::1 remote-as 65100
neighbor 2001::23:C802:CFF:FE78:38
remote-as 65000
neighbor 2002:0:4:1::4 remote-as 65200
neighbor 2002:0:4:1::4 ebgp-multihop 5
neighbor 2002:0:4:1::4 update-source
Loopback0
!
address-family ipv6
no synchronization
network 2002:0:3:2::3/128
network 2002:0:3:3::3/128
neighbor 2001:0:0:13::1 activate
neighbor 2001::23:C802:CFF:FE78:38
activate
neighbor 2001::23:C802:CFF:FE78:38
next-hop-self
neighbor 2002:0:4:1::4 activate
exit-address-family
!
ipv6 route 2001:0:0:34::4/128 Serial1/0
ipv6 route 2002:0:4:1::4/128 Serial1/0
!
ipv6 router ospf 1
router-id 3.3.3.3
log-adjacency-changes
!
MED is RFC compliant non-transitive attribute. It is used for changing a router decision for selecting a path when same routes are learn by eBGP neighbors from a single neighbor AS in multi-homed environment. Lower the MED value, better the path is.
Note 1: In above topology OSPFv3 has been run over R1, R2 and R3 within same area AREA 0.
Note 2: Static routes has been used between R3 and R4 for reachability.
Verification:
R1#sh bgp ipv6 unicast
BGP table version is 11, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
*> 2002:0:1:2::1/128 :: 0 32768 i
*> 2002:0:1:3::1/128 :: 0 32768 i
*> 2002:0:2:2::2/128 2001:0:0:13::3 0 0 65000 i
* 2002:0:2:1::2 0 0 65000 i
*> 2002:0:2:3::2/128 2001:0:0:13::3 0 0 65000 i
* 2002:0:2:1::2 0 0 65000 i
* 2002:0:3:2::3/128 2002:0:2:1::2 0 0 65000 i
*> 2001:0:0:13::3 0 0 65000 i
* 2002:0:3:3::3/128 2002:0:2:1::2 0 0 65000 i
*> 2001:0:0:13::3 0 0 65000 i
* 2002:0:4:2::4/128 2002:0:2:1::2 0 0 65000 65200 i
*> 2001:0:0:13::3 0 0 65000 65200 i
* 2002:0:4:3::4/128 2002:0:2:1::2 0 0 65000 65200 i
*> 2001:0:0:13::3 0 0 65000 65200 i
Here the best paths selected by BGP are via R3.
Modifications on R1
R1(config)#router bgp 65100
R1(config-router)#address-family ipv6
R1(config-router-af)#neigh 2001:0:0:13::3 route-map MED in
R1(config-router-af)#^Z
R1(config)#route-map MED permit 10
R1(config-route-map)#set metric 60 (Will increase the metric of routes by 60)
R1(config-route-map)#exit
R1(config)#route-map MED permit 20
R1(config-route-map)#exit
R1(config)#^Z
R1#clear bgp ipv6 unicast 2001:0:0:13::3
Verification:
R1#sh bgp ipv6 unicast
BGP table version is 35, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network Next Hop Metric LocPrf Weight Path
*> 2002:0:1:2::1/128 :: 0 32768 i
*> 2002:0:1:3::1/128 :: 0 32768 i
* 2002:0:2:2::2/128 2001:0:0:13::3 60 0 65000 i
*> 2002:0:2:1::2 0 0 65000 i
* 2002:0:2:3::2/128 2001:0:0:13::3 60 0 65000 i
*> 2002:0:2:1::2 0 0 65000 i
* 2002:0:3:2::3/128 2001:0:0:13::3 60 0 65000 i
*> 2002:0:2:1::2 0 0 65000 i
* 2002:0:3:3::3/128 2001:0:0:13::3 60 0 65000 i
*> 2002:0:2:1::2 0 0 65000 i
* 2002:0:4:2::4/128 2001:0:0:13::3 60 0 65000 65200 i
*> 2002:0:2:1::2 0 0 65000 65200 i
* 2002:0:4:3::4/128 2001:0:0:13::3 60 0 65000 65200 i
*> 2002:0:2:1::2 0 0 65000 65200 i
Weight has been increased by 60 for the route updates learned via R3 (2001:0:0:13::3) and hence paths via R2 (2002:0:2:1::2) become best paths.