BGP load balancing

[NAVIN PARWAL]

This is what i found on sprint bgp policy page.

Sprint reserves the right to aggregate any announcement for a network smaller than /19 when advertising to external peers such as AT&T, UUnet etc"

if they are agregating then how will they be the preferred path?

Thanks

"

[mheusinger]

Hello,

they will not be the prefered path, if they do it. Longest match is then favouring the unaggregated announcement through a different AS.

In case they are causing you a problem then you need to contact them. In the end you are the customer and are paying for the service.

I think this should only be done for PA address space.

Hope this helps! Please rate all posts.

Regards, Martin

[NAVIN PARWAL]

martin,

How is it done in the real world then?

lets assume that sprint has 100.100.x.x/16 addresss space, and it is giving out 100.100.x.x/24 to its bgp customers? will it advertise /16 and /24 or what?

please help.

i will surely post this thread.

[NAVIN PARWAL]

is it true that all tier 1 ISPs block prefixs greater than /19.

if that is the case, why do people use BGP for load balancing, becuase it is not going to work for loadbalaning is they have a /24.

Thanks

[mheusinger]

Hello,

well this is not so simple. The accepted prefix length depends on the address range. It reflects more or less the registry assignements. Be aware however, that each AS is first of all autonomous. So in principle you could to whatever you like with respect to IP routing, aggregation and the like. There are however some best practices and also good will is needed otherwise internet is not operational ;-)

In case you want to look for yourself into BGP routers of different ISPs then have a look at traceroute.org and follow the link to Route Servers.

Hope this helps! Please rate all posts.

Regards, Martin

[mheusinger]

Hello,

best practice is to announce the IP address blocks the way you get them from the registry. So 100.100.0.0/16 would be announced to the peering partners.

This will not cause any harm to the customer, because you will not be able to announce Sprint IP addresses through another (decent) ISP anyhow. And within the sprint network the detailed routes are present in BGP. Aggregation is done when peering "to the internet".

Hope this helps! Please rate all posts.

Regards, Martin

[NAVIN PARWAL]

Martin,

Do tier 1 ISPs block

lets say that i am using bgp to connect to ISP A and ISPB. which are connected to tier 1 ISP which is blocking

so when i advertise my /24 using bgp for load balancing through ISPA. ISPA only advertises the agregate to Tier 1 ISP and Tier 1 block /24 from ISPA and ISPB. right?

so if i loose the path from ISPA, i loose connection to the internet(inbound). as Tier 1 will not route the traffic through ISPB as it is blocking prefixes greater than /19.

Thanks

[groupcisco]

I dont think Tier1 ISPs block =/24 as some ISP's block

Please rate if helps,

Rgds,

Naveen B