Advertising Multiple Networks with BGP

[patrick.peters]

I'm getting ready to change my IPv4 address space over to a new provider.  I run BGP with multiple ISPs, so I figured I'd just start advertising the new network in my BGP configuration (in addition to my existing network) and slowly migrate my services from one address space to another.

I added the network statement for the new IPv4 class C network and noticed the first strange thing.  I added

network 207.191.52.0 mask 255.255.255.0

but when I do a "show run" I see

router bgp 14385
 no synchronization
 bgp log-neighbor-changes
 network 63.94.231.0 mask 255.255.255.0
 network 207.191.52.0

The mask I specified seems to have for my new network seems to have gone away.  If I look at the routes I'm advertising to my neighbors, I also see unexpected results:

#sho ip bgp nei  207.235.39.229 advertised-routes
BGP table version is 5029, local router ID is 207.235.39.230
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
*> 63.94.231.0/24   0.0.0.0                  0         32768 i
*> 207.191.52.0     0.0.0.0                  0         32768 i

Total number of prefixes 2

Once again, the mask for my new network seems to be missing.

I've done a soft reset with my neighbors.  None of the looking glass servers I have queried seem to see an advertisement for my new network.

My full BGP configuration:

router bgp 14385
 no synchronization
 bgp log-neighbor-changes
 network 63.94.231.0 mask 255.255.255.0
 network 207.191.52.0
 neighbor 64.47.18.173 remote-as 19855
 neighbor 64.47.18.173 soft-reconfiguration inbound
 neighbor 64.47.18.173 filter-list 22 out
 neighbor 66.55.46.182 remote-as 7224
 neighbor 66.55.46.182 password 7 xxxxxxx
 neighbor 207.235.39.229 remote-as 4323
 neighbor 207.235.39.229 soft-reconfiguration inbound
 neighbor 207.235.39.229 filter-list 22 out
 no auto-summary

ip as-path access-list 22 permit ^$

I'm running:

Cisco IOS Software, 2800 Software (C2800NM-SPSERVICESK9-M), Version 15.0(1)M6, RELEASE SOFTWARE (fc1)

on a 2811 router.

I'm at a loss for why this network isn't being picked up by my ISP's, but I'm guessing it has something to do with that subnet mask.  Any suggestions are appreciated.  I don't work with BGP very often, so I'm a little rusty...

Thanks!

[Scott Strickland · Accepted solution]

Patrick,

You are seeing this because your network, 207.191.52.0/24 is a Class C network so BGP is leaving the mask off.  If you were to advertise 207.191.52.0/29, you would see the mask in your advertisement and in the BGP table.  Here is a snippet that shows what I'm referring to:

R10#show run int lo207
Building configuration...

Current configuration : 68 bytes
!
interface Loopback207
 ip address 207.191.52.1 255.255.255.0
end

R10#show run int lo208
Building configuration...

Current configuration : 70 bytes
!
interface Loopback208
 ip address 208.191.52.1 255.255.255.248
end

R10#show run | sec router bgp
router bgp 10
 bgp log-neighbor-changes
 network 207.191.52.0
 network 208.191.52.0 mask 255.255.255.248
 neighbor 155.1.108.8 remote-as 8
R10#
R10#
R10#show ip bgp neighbor 155.1.108.8 advertised-routes
BGP table version is 3, local router ID is 150.1.10.10
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  207.191.52.0     0.0.0.0                  0         32768 i
 *>  208.191.52.0/29  0.0.0.0                  0         32768 i

Total number of prefixes 2 

Scott

[patrick.peters]

Thanks!  It's good to know that I didn't mess up the config. 

Now I just need to figure out why the advertisement doesn't seem to be propagating..  But that's a whole different issue.

[paul driver · Accepted solution]

Hello

Thats becasue the 207 191.52.0 is by default a class c network and it doesnt require a subnet mask statement

If this class C address that was being cidr'd ( i giuess this isnt te correct terminology) using a different subnet range other than the default 24 network bits then you would need to add the subnet mask in the bgp process.

res

Paul

[patrick.peters]

Thanks!  It's good to know that I didn't mess up the config. 

Now I just need to figure out why the advertisement doesn't seem to be propagating..  But that's a whole different issue.