Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

BGP Design Question

Our proposed setup is the following. We are using the same ISP.

Corp RTR---->ISP (20MB)

|

| 100MB Metro LAN

|

DR RTR---->ISP (20MB)

We have been assigned a /24 block from our ISP and I would like to know the best design to load balance and failover to the Metro LAN in the event of a failure.

Am I correct in following the documentation from the link below?

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf3

Thanks in advance.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: BGP Design Question

Hello Igor,

I see.

I guess you have split the public /24 address block in two or more parts internally in your domain and that edge routers are advertising the /24 as a result of using an aggregate address or a static route to null0 for the /24 IP network.

if the ISP is only one you could try to setup an agreement in order to send also specific /25 routes with them.

the other /25 could be advertised with your own AS prepending

so it could be:

COrp: sends out first /25, aggregate /24 second /25 with As path prepending

Hosting: sends out second /25, aggregate /24, first /25 with AS path prepending

Example:

ip prefix-list firstblock seq 5 permit x.y.z.0/25

route-map CorpToISP permit 10

match ip address prefix firstblock

set as-path prepend yourAS yourAS

route-map CorpToISP permit 20

! second empty block to advertise the other prefixes

router bgp yourAS

neigh ISP-ipaddress route-map CorpToISP out

Hope to help

Giuseppe

5 REPLIES
Hall of Fame Super Silver

Re: BGP Design Question

Hello Igor,

you are correct in following that link an iBGP session over the metro ethernet link is useful in this case

if DR site should be used only used for failover you could use MED and As path prepending to make the first link the primary link.

route-map fromDRtoISP permit 10

set metric 500

set as-path prepend yourAS yourAS

DR router

router bgp yourAS

neigh ISP route-map fromDRtoISP out

Hope to help

Giuseppe

New Member

Re: BGP Design Question

Giuseppe,

I should change DR to Hosting. Our end goal is to host clients and load balance our links as our /24 netblock will be used for clients at the hosting center and for our company at our HQ.  In case of either Internet link failing, we would need traffic to use the other Internet link and the metro link.

Hope this makes sense.

Thanks

Hall of Fame Super Silver

Re: BGP Design Question

Hello Igor,

I see.

I guess you have split the public /24 address block in two or more parts internally in your domain and that edge routers are advertising the /24 as a result of using an aggregate address or a static route to null0 for the /24 IP network.

if the ISP is only one you could try to setup an agreement in order to send also specific /25 routes with them.

the other /25 could be advertised with your own AS prepending

so it could be:

COrp: sends out first /25, aggregate /24 second /25 with As path prepending

Hosting: sends out second /25, aggregate /24, first /25 with AS path prepending

Example:

ip prefix-list firstblock seq 5 permit x.y.z.0/25

route-map CorpToISP permit 10

match ip address prefix firstblock

set as-path prepend yourAS yourAS

route-map CorpToISP permit 20

! second empty block to advertise the other prefixes

router bgp yourAS

neigh ISP-ipaddress route-map CorpToISP out

Hope to help

Giuseppe

New Member

Re: BGP Design Question

Giuseppe

Can you explain this command in more detail?

route-map CorpToISP permit 20

! second empty block to advertise the other prefixes

Hall of Fame Super Silver

Re: BGP Design Question

Hello Igor,

it is simply an empty route-map clause to be used to advertise the other IP prefixes to eBGP neighbor

route-map CorpToISP permit 20

>> ! second empty block to advertise the other prefixes

this is just a comment sorry if it caused confusion

Hope to help

Giuseppe

247
Views
0
Helpful
5
Replies