Basic question on route not in BGP routing table

Answered Question
Mar 31st, 2010

On Router1 I do:

router bgp 100

neighbor 1.1.1.1 remote-as 200

network 10.177.110.0 mask 255.255.255.0

network 10.177.330.0 mask 255.255.255.0

I do 'show ip bgp' and route 10.177.110.0 is advertised OK but 10.177.330.0 is not.

Then I did 'show ip route 10.177.330.0' and it stated:

Routing entry for 10.177.330.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan3
      Route metric is 0, traffic share count is 1

Then I notice that such '10.177.330.0/24' is advertised under the 'router osp[f 1' on Router1.

Question:
If this is learned via connected or IGP, shouldn't this network also get installed on the BGP routing table?

I do not understand why I do not see 10.177.330.0 under 'show ip bgp'.

Correct Answer by Giuseppe Larosa about 6 years 10 months ago

Hello Marlon,

>>10.177.330.0/24

as far as I know 330 is not a valid value for an IPv4 address that is formed by 32 bits written as 4 dotted decimal bytes so each value is in range 0-255

By the way,

one possible reason could be that  the network command is mismatching in at least one bit with effective ip address on interface

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Wed, 03/31/2010 - 08:08

Hello Marlon,

>>10.177.330.0/24

as far as I know 330 is not a valid value for an IPv4 address that is formed by 32 bits written as 4 dotted decimal bytes so each value is in range 0-255

By the way,

one possible reason could be that  the network command is mismatching in at least one bit with effective ip address on interface

Hope to help

Giuseppe

news2010a Wed, 03/31/2010 - 08:27

Very sorry for the bad edit. It is:

>>10.177.130.0/24

It is 10.177.130.0/24.

Aaron Harrison Wed, 03/31/2010 - 08:35

Well - it's probably best if you copy/paste your actual router output in rather than editing it.

If we can't see the actual config we probably can't see the actual problem.

Aaron

news2010a Wed, 03/31/2010 - 14:32

My apologies again for the confusion. I will promise to myself I will only paste info on this forum from now on. :-)

However, Giuslar hit the nail once again.

I was told to advertise network 10.177.130.0/24 via BGP to ISP.

However, there is no 10.177.130.0/24 in the ip routing table.

I see that I have 10.177.130.0/27 in the routing table.


So that means that once I advertised 10.177.130.0/24 via BGP, since there is no exact match in the routing table, the prefix was not advertised via BGP.

So I will have to consult the ISP and confirm the mask given to me was wrong I guess...

gw1#show ip bgp 10.177.130.0 255.255.255.0
% Network not in table
gw1#show ip route 10.177.130.0
Routing entry for 10.177.130.0/27
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan3
      Route metric is 0, traffic share count is 1

gw1#show ip bgp 10.177.130.0
% Network not in table


Ronit Bhattacharjee Wed, 03/31/2010 - 11:29

Hmm.. Very fishy.. you;ve mentioned 330 everythwre in the show commands.. Which means you have not copy pasted the whole thing but typed it all in by yourself.. This can lead to erronous data

Also, you have mentioned that it shows up as advertised in OSPF, which we don't see in the "show ip route" you've supplied here

Would appreciate if you can get the original "show ip route", "show run".

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