bgp 1 part 2...

ita advertises routes for each of its connected neighbors, isp1 and isp2... these routes are added to the respective route tables, which could cause either to route traffic through ita... the lab wants to advertise only routes that belong to ita (ita stands for international travel agency, btw, not my idea), namely the 192.168 loopbacks...

isp1#sh ip route bgp

Gateway of last resort is not set

      172.16.0.0/24 is subnetted, 1 subnets
B        172.16.1.0 [20/0] via 10.0.0.2, 22:17:15
B     192.168.0.0/24 [20/0] via 10.0.0.2, 22:17:45
B     192.168.1.0/24 [20/0] via 10.0.0.2, 22:17:45
isp1#

isp2#sh ip route bgp

Gateway of last resort is not set

      10.0.0.0/24 is subnetted, 1 subnets
B        10.1.1.0 [20/0] via 172.16.0.2, 22:03:41
B     192.168.0.0/24 [20/0] via 172.16.0.2, 22:18:13
B     192.168.1.0/24 [20/0] via 172.16.0.2, 22:18:13

we'll make an acl and distribute...

access-list 1 permit 192.168.0.0 0.0.1.255

permitting only the loopbacks...

router bgp 100
neighbor 10.0.0.1 distribute-list 1 out
neighbor 172.16.0.1 distribute-list 1 out

distribute only the address in acl 1 out to each neighbor... perfect...

then clear the table...

this is disruptive, breaking the tcp connections...

ita#
*Aug 20 17:46:28: %BGP-5-ADJCHANGE: neighbor 10.0.0.1 Down User reset
*Aug 20 17:46:28: %BGP_SESSION-5-ADJCHANGE: neighbor 10.0.0.1 IPv4 Unicast topology base removed from session  User reset
*Aug 20 17:46:28: %BGP-5-ADJCHANGE: neighbor 172.16.0.1 Down User reset
*Aug 20 17:46:28: %BGP_SESSION-5-ADJCHANGE: neighbor 172.16.0.1 IPv4 Unicast topology base removed from session  User reset
*Aug 20 17:46:29: %BGP-5-ADJCHANGE: neighbor 10.0.0.1 Up
*Aug 20 17:46:29: %BGP-5-ADJCHANGE: neighbor 172.16.0.1 Up
ita#

but, you get this...

isp1#sh ip route bgp

Gateway of last resort is not set

B     192.168.0.0/24 [20/0] via 10.0.0.2, 00:29:53
B     192.168.1.0/24 [20/0] via 10.0.0.2, 00:29:53

isp2#sh ip route bgp

Gateway of last resort is not set

B     192.168.0.0/24 [20/0] via 172.16.0.2, 00:30:34
B     192.168.1.0/24 [20/0] via 172.16.0.2, 00:30:34

much cleaner...

you want to make isp1 your primary provider, designating isp2 as the backup... this can be accomplished by using a floating static route...
ita#sh ip route | excl L | incl Loop
    
Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C        10.0.0.0/24 is directly connected, Serial1/1
B        10.1.1.0/24 [20/0] via 10.0.0.1, 00:47:49
      172.16.0.0/16 is variably subnetted, 3 subnets, 3 masks
C        172.16.0.0/30 is directly connected, Serial1/2
B        172.16.1.0/24 [20/0] via 172.16.0.1, 00:47:49
      192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.0.0/24 is directly connected, Loopback0
      192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.1.0/24 is directly connected, Loopback1

from the output we see that there is no gateway of last resort and the metrics are equal... this solution is icky...

ip route 0.0.0.0 0.0.0.0 10.0.0.1 210
ip route 0.0.0.0 0.0.0.0 172.16.0.1 220


preferring the default of isp1... (i just threw up in my mouth)


ita#sh ip route | excl L | incl Loop
     
Gateway of last resort is 10.0.0.1 to network 0.0.0.0

S*    0.0.0.0/0 [210/0] via 10.0.0.1
      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C        10.0.0.0/24 is directly connected, Serial1/1
B        10.1.1.0/24 [20/0] via 10.0.0.1, 00:51:59
      172.16.0.0/16 is variably subnetted, 3 subnets, 3 masks
C        172.16.0.0/30 is directly connected, Serial1/2
B        172.16.1.0/24 [20/0] via 172.16.0.1, 00:51:59
      192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.0.0/24 is directly connected, Loopback0
      192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.1.0/24 is directly connected, Loopback1

or use default-originate... get rid of the floaters...

isp1(config)#router bgp 200
isp1(config-router)#neighb 10.0.0.2 default-originate

ita#sh ip route | excl L | incl Loop
      
Gateway of last resort is 10.0.0.1 to network 0.0.0.0

B*    0.0.0.0/0 [20/0] via 10.0.0.1, 00:00:12
      10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C        10.0.0.0/24 is directly connected, Serial1/1
B        10.1.1.0/24 [20/0] via 10.0.0.1, 01:03:32
      172.16.0.0/16 is variably subnetted, 3 subnets, 3 masks
C        172.16.0.0/30 is directly connected, Serial1/2
B        172.16.1.0/24 [20/0] via 172.16.0.1, 01:03:32
      192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.0.0/24 is directly connected, Loopback0
      192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.1.0/24 is directly connected, Loopback1

it can be done with default-network also but that is yet more artificial than the floating static... default-originate is the elegant solution...