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Community Member

How to Rx default originate only - BGP

Hi,

We have eBGp with our SP and they are sending default to us. When we do a show ip bgp ne X.X.X.X received-routes the O/P says % Inbound soft reconfiguration not enabled on X.X.X.X.

If I do a Soft reconfiguration on the Inbound. It learns a whole lot of routes along with default even if i have a distribute list for the neighbor with deny any which looks like

neighbor X.X.X.X distribute-list 2 in

access-list 2 deny any

Please let me know

1. How do i get only the default.

2. What all events will trigger our SP's Border Gateway to stop sending the default.

Thanks in advance,

subra

9 REPLIES
Cisco Employee

Re: How to Rx default originate only - BGP

Subra,

access-list 2 permit 0.0.0.0

access-list 2 deny any

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Community Member

Re: How to Rx default originate only - BGP

Hi,

THanks for the info.

I get the following from the sh ip bgp neighbor

Network Next Hop Metric LocPrf Weight Path

r> 0.0.0.0 X.X.X.X 0 65535 i

What could be wrong now?

r -> rib failure.

I am running cat 4500. below is the show ver:

Cisco IOS Software, Catalyst 4500 L3 Switch Software (cat4500-ENTSERVICESK9-M), Version 12.2(46)SG, RELEASE SOFTWARE (fc1)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2008 by Cisco Systems, Inc.

Compiled Fri 27-Jun-08 16:24 by prod_rel_team

Image text-base: 0x10000000, data-base: 0x11E3C0D8

ROM: 12.2(31r)SGA1

Pod Revision 14, Force Revision 31, Tie Revision 32

Telecity_Border_1 uptime is 9 weeks, 4 days, 9 hours, 53 minutes

System returned to ROM by power-on

System image file is "bootflash:cat4500-entservicesk9-mz.122-46.SG.bin"

This product contains cryptographic features and is subject to United

States and local country laws governing import, export, transfer and

use. Delivery of Cisco cryptographic products does not imply

third-party authority to import, export, distribute or use encryption.

Importers, exporters, distributors and users are responsible for

compliance with U.S. and local country laws. By using this product you

agree to comply with applicable laws and regulations. If you are unable

to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to

export@cisco.com.

cisco WS-C4506 (MPC8540) processor (revision 13) with 524288K bytes of memory.

Processor board ID FOX06460YN3

MPC8540 CPU at 800Mhz, Supervisor V-10GE

Last reset from PowerUp

1 Virtual Ethernet interface

58 Gigabit Ethernet interfaces

2 Ten Gigabit Ethernet interfaces

511K bytes of non-volatile configuration memory.

Configuration register is 0x101

Thanks in advance

Community Member

Re: How to Rx default originate only - BGP

Hi,

I got it. it was due to a lower AD static route already installed. after removing it. I got it working.

Thanks hritter for your help.

Can some one help me with my second doubt.

Blue

Re: How to Rx default originate only - BGP

Your second dounbt? Do you mean question?

Hall of Fame Super Bronze

Re: How to Rx default originate only - BGP

What all events will trigger our SP's Border Gateway to stop sending the default.

When the BGP router no longer has the 0.0.0.0/0 on its routing table.

__

Edison.

Community Member

Re: How to Rx default originate only - BGP

Thanks for your time.

Does it mean that my SP BG Router has a Default originate from its upstream as well.

Cheers

Subra

Hall of Fame Super Bronze

Re: How to Rx default originate only - BGP

Does it mean that my SP has a Default originate from its upstream as well.

Hard to tell what the SP may have but there are several ways on how to inject a 0.0.0.0 into BGP or advertise the 0.0.0.0 to a neighbor for that matter.

The SP may have a dynamic or static default route along with the network 0.0.0.0 under BGP.

The SP may also have a dynamic or static default route along with a distribution information originate under BGP.

or

The SP may have an unconditional default originate on the neighbor statement pointing towards you.

On the latter approach, they don't need to have the 0.0.0.0 in the routing table.

It will advertise the 0.0.0.0 all the time.

HTH,

__

Edison.

Community Member

Re: How to Rx default originate only - BGP

Thanks again.

I would like to know, if for some reason my SP's BGP peering fails with any other T1 SP or fails to learn the routes from its upstream will it be still sending me a default originate (in case of unconditionally sending default originate). What should i do to overcome this. Please help me clear this doubt.

cheers

Subra

Hall of Fame Super Bronze

Re: How to Rx default originate only - BGP

Subra,

The best way to know is asking the provider. Each provider will have different BGP policies on how they handle the network advertisement to customers.

If you still want to send your traffic towards the ISP even if they don't send 0.0.0.0/0 network, then you can configure a floating default route towards that same ISP. However, if they aren't sending the 0.0.0.0/0 - you may as well drop it locally.

__

Edison.

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