BGP Multihoming - different providers

Answered Question
Nov 24th, 2009
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Hi Experts,


As of now we have single internet provider to my DC and we have public IP pool (195.34.56.0/24 leased from old provider)
Now we take another internet provider for redundancy and we bought one public IP pool (193.141.24.0/24)


I have two my routers (1841) in hsrp at my DC, both providers have their own routers at perimeter network at my DC.

Both new and Old internet lines are ready to use, now I have to do BGP multihoming on my both hsrp routers and I dont want use IP pool 195.34.56.0 which taking leased from old provider.


At present I have my own two public IP pools those are 193.141.24.0/24 and 193.143.209/20


Experts can someone guide me how I have to proceed with Mutlihoming and what are the steps I have to follow and how to configure and all...


Thanks in advance.

Regards,
Naidu.

Correct Answer by Giuseppe Larosa about 7 years 6 months ago

Hello Naidu,

some safety measures have to be added :


use route filters to decide what you are willing to accept from each provider.

use an as path access-list to be sure you will never act as a transit between the two providers



example:

you want to accept only a default route


ip prefix-list only-default permit 0.0.0.0/0


route-map fromISP1 permit 10

match ip address prefix only-default



route-map fromISP2 permit 10

match ip address prefix only-default


ip as-path access-list 11 permit ^$


route-map toISP1 permit 10

match as-path 11


route-map toISP2 permit 10

match as-path 11


router bgp your.ASN

neigh ISP1.ipaddress route-map fromISP1 in

neigh ISP1.ipaddress  route-map toISP1 out

neigh ISP2.ipaddress route-map fromISP2 in

neigh ISP2.ipaddress route-map toISP2 out






It is better to have separated route-maps you may want to make changes in the future



Hope to help

Giuseppe

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ilnaiduccna Wed, 11/25/2009 - 06:16
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Hi Giuseppe,


Thanks for your response.


I too have the same document, what I would like to request you is if you have experienced in BGP multihoming and I want your best suggestions how to go towards success on this.


Can you provide me If you have any kind of templete.



Thanks & Regards,

Naidu.

Correct Answer
Giuseppe Larosa Wed, 11/25/2009 - 10:11
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Hello Naidu,

some safety measures have to be added :


use route filters to decide what you are willing to accept from each provider.

use an as path access-list to be sure you will never act as a transit between the two providers



example:

you want to accept only a default route


ip prefix-list only-default permit 0.0.0.0/0


route-map fromISP1 permit 10

match ip address prefix only-default



route-map fromISP2 permit 10

match ip address prefix only-default


ip as-path access-list 11 permit ^$


route-map toISP1 permit 10

match as-path 11


route-map toISP2 permit 10

match as-path 11


router bgp your.ASN

neigh ISP1.ipaddress route-map fromISP1 in

neigh ISP1.ipaddress  route-map toISP1 out

neigh ISP2.ipaddress route-map fromISP2 in

neigh ISP2.ipaddress route-map toISP2 out






It is better to have separated route-maps you may want to make changes in the future



Hope to help

Giuseppe

ilnaiduccna Thu, 11/26/2009 - 02:33
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Hi Guiseppe,

Nice to see your reply and good explanation .


As of now the BGP multihoming configured and maintain will be by Provider itself.


Yes, I would like to point only default route to provider GW.

say 0.0.0.0 0.0.0.0 197.28.56.1


I hope the ip as-path access-list can configure on my routers, to not accept any other AS from internet; is that right?


I couldn't understand......

you want to accept only a default route

ip prefix-list only-default permit 0.0.0.0/0


You mean shall I accept default route, which means the whole default route from internet?

Please correct me if I am wrong.


Thanks in advance,


Regards,

Naidu.


Giuseppe Larosa Thu, 11/26/2009 - 03:26
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Hello Naidu,

yes the idea is to accept a BGP route 0.0.0.0/0 that is a default route from providers routers


using a default static route is not recommended because your router cannot know when one router has a problem (indirect failure)



your router sends your public IP blocks and you receive a default BGP route


Hope to help

Giuseppe

ilnaiduccna Thu, 11/26/2009 - 06:19
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Hi Giuseppe,


Oh....great...!


I have small doubts.


If we accept a default route from providers, will it be not accept like whole internet routing table like that?


If that is not the case, I heard sometimes the whole internet routing table will land on our routers then router get crash like that because of some miss configuration; is that right?


In what situations will be like that happen, what could be the causes to came whole internet routing table to our router?


Is there any specific BGP default route like that? (yes the idea is to accept a BGP route 0.0.0.0/0 that is a default route from providers routers)


Can you please clear me.



Thanks & Regards,

Naidu.

Giuseppe Larosa Thu, 11/26/2009 - 06:40
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Hello Naidu,

the proposed input route filter has the objective to accept only the default route that is a single BGP prefix.


a full routing table is made of 300,000 routes nowdays and cannot be handled by your router.


accepting a default route means accepting only special prefix 0.0.0.0/0 as I wrote so your router shouldn't be overhwhelmed by it.



Hope to help

Giuseppe

Athiqur Rahman Wed, 04/07/2010 - 08:11
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Hi Giuseppe,


picking up on your point about not adding a default static route but to accept static route from ISP. In multi homed network how would you make it so the one ISP is higher priority and used as default exit point. If the main ISP fails then the default gateway should be to the second ISP?


Thanks

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