BGP default route route-map

[Krasnoperov]

Please advise

I have BGP peer with upstaream ISP

I need recieve default route only

I want to do this via route-map with prefix-list (not just perfix-list)

How can I do this?

Now I do next (but it doesn't work)

router bgp 5xxxx

bgp log-neighbor-changes

bgp deterministic-med

neighbor 193.xxx.zzz.xx remote-as 900

neighbor 193.xxx.zzz.xx description ISP UpStream

neighbor 193.xxx.zzz.xx version 4

address-family ipv4

  network 193.0.0.0 mask 255.255.252.0

  neighbor 193.xxx.zzz.xx activate

  neighbor 193.xxx.zzz.xx soft-reconfiguration inbound

  neighbor 193.xxx.zzz.xx route-map map-900-ISP-in in

  neighbor 193.xxx.zzz.xx route-map map-900-ISP-out out

sh route-map map-900-ISP-in

route-map map-900-ISP-in, permit, sequence 30

  Match clauses:

    ip address prefix-lists: def_only

  Set clauses:

  Policy routing matches: 0 packets, 0 bytes

route-map map-900-ISP-in, permit, sequence 40

  Match clauses:

  Set clauses:

    local-preference 90

  Policy routing matches: 0 packets, 0 bytes

sh ip prefix-list def_only

ip prefix-list def_only: 2 entries

   seq 15 deny 0.0.0.0/0 ge 1

   seq 20 permit 0.0.0.0/0

[cadet alain · Accepted solution]

Hi,

get rid of the permit 30 statement in your inbound route-map

Regards.

Alain

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[smitesh kharecha]

Hi Cadet,

Not too sure how removing seq 30 will resolve the issue. As seq 30 is for prefix list.

If we go by the route-map, it will first match AS-PATH list 1 ( which is permiting couple if as-path) and will deny it.

Then it will logically ORed with seq 30 ( which is prefix list ) allowing only 0.0.0.0/0.

And then it will logically ORed with seq 40 ( which doesn't have anything in it).

So based on the above logic, if any one of the condition matches, it will exit out of the route-map.

Regards,

Smitesh

[cadet alain]

Hi,

in BGP if you  specify a catch-all route-map statement then everything not matched by previous statements will get matched by this one.

to get a AND logic and not OR logic you would have to get more than one match action in a single statement( permit or deny).

Regards.

Alain

Don't forget to rate helpful posts.

[Krasnoperov]

why?

route-map map-900-ISP-in, permit, sequence 30

  Match clauses:

    ip address prefix-lists: def_only

  Set clauses:

exactly this seq for my task

I need receive default only

[blau grana]

Could you please post output from

#sh run | s route-map map-900-ISP-in

[Krasnoperov]

statement 40, thaks this was issue

[smitesh kharecha]

Hi,

Can you please explain, why you have network 193.XX.ZZ.00 mask 255.255.252.0 in your BGP config.

If it is not one of you prefixes, remove that network entry from BGP config.

router bgp 5xxx

address-family ipv4

no network 193.xxx.zzz.00 mask 255.255.252.0

SOFT clear the BGP Peers:

clear ip bgp * soft in

clear ip bgp * soft out

and then check whether issue still persists.

Regards,

Smitesh

[cadet alain]

Hi Smitesh,

can you tell me how having a network command for a prefix can influence what you receive from the ISP when you apply a inbound route-map to filter prefixes?

Also as a sidenote, almost every router supports route-refresh so  no need for the soft keyword anymore in this case.

Regards.

Alain

Don't forget to rate helpful posts.

[smitesh kharecha]

Hi Cadet,

The prefix which he is getting in his BGP table was same which he is advertising.

I expected then that prefix to be something like:

*>193.XX.ZZ.0/22     0.0.0.0     0         32768 i

*                              193.XXZZ.XX

However, his BGP table only showed that he is learning that prefix from his service provider. So I thought if in case if he is not suppose to originate that prefix from his own AS, why was it then advertise from his AS. Hence recommended to remove.

Editted: Very much aware about route-refresh. Just plain old habbit of doing things that way.

Regards,

Smitesh

Message was edited by: smitesh kharecha

[Krasnoperov]

it's my network which I advertise to peer

[smitesh kharecha]

Hi,

If it is your network, it is quit strange that your ISP is advertised it to you showing that prefix as originated from their AS.

Can you please check with your ISP and ask them why they are originating 193.XX.ZZ.00/22 prefix ?

Regards,

Smitesh

[Krasnoperov]

sorry, my misstake when print and change real otput of show command