09-02-2008 08:18 PM - edited 03-03-2019 11:22 PM
hi all,
any one know how RouterA and router B form bgp neighbor by using loopback address
RouterA
loopback 0 = 1.1.1.1/32
serial 1 = 192.168.1.1/24
RouterB
loopback 0 = 2.2.2.2/32
serial 1 = 192.168.1.2 /24
09-02-2008 08:36 PM
firs use the loopback as source update only with ibgp when the nighbors can reach each other through multiple paths so in case of one physical path gose down the other will be used and no route and path recalculation needed because the nighboring based on loop back interfaces which is vitual interface always up
for example
routerA-------routerB first link
second link
routerA---routerC--routerB
so we goona configure router a and b to use loopback address so if the directly link between them goes down they will go through routerC without intruption
keep in mind u need to run IGP between the routers like ospf and advertise the loopback on each router
routerA
router ospf 1
network 192.168.1.0 0.0.0.255 area 0
network 1.1.1.1 0.0.0.0 area 0
also in our example wee need to put the ip of the network with routerC
router bgp 1
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 updtae-source loopback 0
RoterB
router ospf 1
network 192.168.1.0 0.0.0.255 area 0
network 2.2.2.2 0.0.0.0 area 0
also in our example wee need to put the ip of the network with routerC
router bgp 1
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 updtae-source loopback 0
good luck
if helpful Rate
09-02-2008 08:37 PM
For e-BGP
RouterA
router bgp 400
neigbor 2.2.2.2 remote-as 500
neigbor 2.2.2.2 ebgp-multihop 2
neigbor 2.2.2.2 update-source loopback 0
ip route 2.2.2.2 255.255.255.255 192.168.1.2
--------------------------------------------
RouterB
router bgp 500
neigbor 1.1.1.1 remote-as 400
neigbor 1.1.1.1 ebgp-multihop 2
neigbor 1.1.1.1 update-source loopback 0
ip route 1.1.1.1 255.255.255.255 192.168.1.1
--------------------------------------------
For iBGP remove "ebgp-multihop" command ,
HTH..rate if helpful..
09-02-2008 09:14 PM
hi Satish
the command neigbor 1.1.1.1 ebgp-multihop 2 in this case not rquired unless he looks to achieve loadbalncing and have two links with it as well
so in his case h e has only one serial link !!
thank you
09-02-2008 10:24 PM
But rule says "ebgp-multihop" command chnages TTL value , in order to allow the packet to reach the external BGP peer which is not directly connected , or is using an interface other than the directly connected interface , in this case loopback 0 .
correct me if i am wrong..
HTH..rate if useful..
09-02-2008 10:46 PM
it seems fail. any one know the issue ?
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
duplex auto
speed auto
!
router bgp 10
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 20
neighbor 2.2.2.2 update-source Loopback0
!
ip classless
ip route 2.2.2.2 255.255.255.255 192.168.1.2
ip http server
R0#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 10
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
2.2.2.2 4 20 0 0 0 0 0 never Idle
*********************************88
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet0/0
ip address 192.168.1.2 255.255.255.0
duplex auto
speed auto
!
router bgp 20
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 10
neighbor 1.1.1.1 update-source Loopback0
!
ip classless
ip route 1.1.1.1 255.255.255.255 192.168.1.1
09-02-2008 10:49 PM
Use "neighbor x.x.x.x ebgp-multihop 2" on both sides and then see.
09-03-2008 07:47 AM
Marwan,
ebgp-multihop is required whenever you want to establish a BGP session to a peer address belonging to a non-directly connected subnet.
I think you are reffering to maximum-path. maximum-path is only required if you receive the same prefix from than one peer and want to use all of them for load-balancing purposes.
Regards,
09-03-2008 06:28 PM
hi HAROLD
thanks and as u said it mixed up the commands :)
anyway regarding the use of loopback adress as update source i think it is better with EBGP to use the next-hop interface IP instead of the loopback address
becuase in large bgp deployment u need to get the loopback advertised to all peers to get the binefit of it ! while with IBGP just advertise it through the IGP and it will work as expected
do you agree with me HAROLD ?
thanks again
09-04-2008 06:28 AM
Marwan,
I do agree that eBGP session are usually established using the physical address IP addresses as the source and destination. The configuration of the loopback addresses as the source and destination is mostly used in the case there is multiple links between the two routers and you want load balancing to take place.
Regards
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