BGP Configuration ASA - Understanding BGP Route format

Routing & Switching BGP
1

I have cisco ASA based topology as follows :

ASA1-7.7.7.3/24---------bgp--------7.7.7.4/24–ASA2

Its is a bgp protocol running and two ASAs are connected via direct link in subnet 7.7.7.0/24 . ASA2-bgp advertise 0/0 network using network command

As a result , ASA1 install the following route, as shown by using show route cmd

B* 0.0.0.0 0.0.0.0 [20/0] via 7.7.7.4, 04:04:00

Where is an outgoing interface in the above route ? Is this recursive route ?

If pkt with unknown destination arrives on ASA1, how it will know which interface to send out pkt ?

Pasting the Complete routing table on ASA1for a reference.

B       0.0.0.0 0.0.0.0 [20/0] via 7.7.7.4, 06:04:07
S        4.4.4.0 255.255.255.0 [1/0] via 84.1.97.212, outside_0_5
C        5.5.5.0 255.255.255.0 is directly connected, outside_0_1
L        5.5.5.3 255.255.255.255 is directly connected, outside_0_1
C        6.6.6.0 255.255.255.0 is directly connected, outside_0_2
L        6.6.6.3 255.255.255.255 is directly connected, outside_0_2
C        7.7.7.0 255.255.255.0 is directly connected, outside_0_3
L        7.7.7.3 255.255.255.255 is directly connected, outside_0_3
C        9.9.9.0 255.255.255.0 is directly connected, vti2
L        9.9.9.1 255.255.255.255 is directly connected, vti2
C        84.1.97.0 255.255.255.0 is directly connected, outside_0_5
L        84.1.97.213 255.255.255.255 is directly connected, outside_0_5
C        84.1.98.0 255.255.255.0 is directly connected, outside_0_6
L        84.1.98.213 255.255.255.255 is directly connected, outside_0_6
C        84.1.99.0 255.255.255.0 is directly connected, outside_0_7
L        84.1.99.213 255.255.255.255 is directly connected, outside_0_7
S        100.1.1.1 255.255.255.255 [1/0] via 84.1.98.212, outside_0_6
C        100.100.4.131 255.255.255.255 is directly connected, lo0
S        122.1.1.2 255.255.255.255 [1/0] via 84.1.97.212, outside_0_5
2

Hello Abhishek

ASA1 will know to send it out of the right interface because recursive routing takes place. Here are the steps:

  1. A packet arrives with a destination IP of, say, 99.1.1.1. This destination will be looked up in the routing table, it won’t be found, and the default route will be chosen.
  2. The default route states that the next hop IP is 7.7.7.4. At this point, a recursive lookup will take place to find out how to get to this next-hop IP.
  3. The recursive lookup of 7.7.7.4 matches the directly connected network on the outside_0_3 interface, so the exit interface is determined.,
  4. The packet is then sent out of the outside_0_3 interface.

For more info on what recursive routing is, take a look at the Routing - what is recursive routing NetworkLessons Note.

I hope this has been helpful!

Laz