Lab 4, Task 2.7. BGP network statements on ASBRs?

Hi,

I have been looking at Lab 4, task 2.7.

The task is to configure IPv4 unicast BGP within and between AS 1000 and 2000.

The task states:

-    Advertise the IPv4 Loopback0 networks of all these devices into BGP
-    One complete there should be full Inter-AS connectivity between all IPv4 Loopback0 networks

As we are running iBGP within both AS 1000 and 2000 it made sense to me to advertise the loopbacks into BGP on the ‘local’ router. For example:

R1:

router bgp 2000
 address-family ipv4
  network 10.0.0.1 mask 255.255.255.255
 
R4:

router bgp 2000
 address-family ipv4
  network 10.0.0.4 mask 255.255.255.255

In the solution guide I see Brian advertised the loopbacks on the ASBR:

R3:

router bgp 2000
 address-family ipv4
  network 10.0.0.1 mask 255.255.255.255
  network 10.0.0.3 mask 255.255.255.255
  network 10.0.0.4 mask 255.255.255.255

Can anyone see any pros/cons to these two designs?

If the internal routers are running iBGP, why not put the network statements on the local router?

Thanks.

Comments

  • Hi mate,

    I followed the next solution and not this as workbook

    R1:

    router bgp 2000
     address-family ipv4
      network 10.0.0.1 mask 255.255.255.255
     
    R4:

    router bgp 2000
     address-family ipv4
      network 10.0.0.4 mask 255.255.255.255

     

    It seems more straight for me each node e.g. R1 to advertise  its local subnet  via bgp network statements than only the ASBR which relies to the IGP - OSPF to learn these subnets.

    Maybe Brian could advice on that!

     

    BR,

    vasilis

     

     

  • A possible reason to configure all the network BGP statements to the ASBR could be that to IOS XR only the originator of a BGP route can allocate labels. If you dont originate the BGP routes via network to the ASBR then the bgp send label has to be activated to the the rest BGP peers. "That’s why in most designs you just have your edge routers originate the BGP networks on behalf of the IGP network, because then you have a single point of control for them."

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