Comments on: Cisco: 2-Bytes / 4-Bytes ASN BGP scenarios

By: Dhana

Dhana — Fri, 30 Sep 2011 18:36:00 +0000

I find this very useful and clear explanation

By: Cory

Cory — Mon, 27 Sep 2010 00:28:34 +0000

Cisco SFP

By: yotis

yotis — Tue, 04 May 2010 18:04:58 +0000

Hello Davison,

What do you mean with "latest IOS"?
I did a simple search with Cisco Software Advisor and it give me 12.4(24)T3 (c3825-adventerprisek9-mz.12.4-24.T3) that it support ASN 4-byte. I went with Enterprise version as I didn't knew what features you need.

Let me know if this helps you!

By: yotis

yotis — Tue, 04 May 2010 18:04:58 +0000

Hello Davison,

Let me know if this helps you!

By: Davison

Davison — Tue, 04 May 2010 12:05:40 +0000

We are trying to run 4 byte as on router 3825 R .And put the latest IOS also..

But its supporting only <1-65535> Autonomous system number.

Can you pleas help me

By: cisco sfp

cisco sfp — Wed, 24 Mar 2010 05:30:47 +0000

Thank you for your post i am quiet new to this but still got some useful information from your blog !

By: Calin

Calin — Thu, 11 Feb 2010 11:52:11 +0000

Hello Kevin.

If you got a 4byte AS then your devices have to support 4byte AS configuration. Otherwise you cannot make it work. 23456, was created with special purpose, so you cannot initialize your BGP session with this AS. It is used only if you have a 2byte ASN capable router and you need to peer with a 4byte ASN.

I believe that if you upgrade your IOS on those 7301 you will get 4byte ASN support. Please contact me if you need more help regarding your issue.

By: Kevin

Kevin — Thu, 11 Feb 2010 11:11:52 +0000

Hi all, We've been asigned a 4byte AS and we now have our own PI space, the externally facing routers are 7301's. I can't give our routers a 4byte AS as 7301's don't support it. Do I need to create an AS in 23456 and somehow pass my 4byte AS ina path attribute, if so how do I do this, the ISP router I'm peering with doesn't support 4byte AS either. Regards Kevin

By: Calin

Calin — Mon, 16 Nov 2009 21:59:31 +0000

Hello Vaib,

According to Cisco the 3750 cannot support yet (or maybe ever) the 4-byte ASN. So you'll have to connect both ISP to that 1841 and apply a basic "single-homed" BGP configuration.You have to establish BGP sessions with both providers and to receive prefixes (or just a default route) from them. Next if you want one to be higher preferred than the other one, or try to achieve some kind of load-balancing, you just have to use some simple route-map for the in / out prefixes.

Since I don't know the details, this is the only advice that I can give to you. If you want more details, contact me over the e-mail and we can discuss.

Good luck!

By: Vaibhav

Vaibhav — Sat, 14 Nov 2009 13:38:59 +0000

Dear Sir,

I must need 4 byte BGP in cisco 3750g 12 SFP port swtich. currently working fine 4 byte BGP in our 1841 router with one ISP Bandwidth 45 MB, now we need 2nd ISP bandwidth for load balance and also when any one ISP bandwidht goes down it’s up automec on wokrig ISP bandwidth. 2nd ISP bandwidth is 30 MB, can it is possible both ISP in our 1841 router if yes , so please what i have to need to upgrade in my router and what is the configuration for two ISP bandwidth in 1841 router for load balance.

can it is possible 4 byte BGP in 3750g 12 SFP port switch any IOS need to upgrade for 4 byte BGP in cisco 3750g switch.

Please help me ASAS.

Thanks in ADV,

Vaib…