[j-nsp] Loopback IP address in BGP Peering

[Mark Tinka]

On Friday 27 February 2009 11:34:42 pm chenoi A wrote:

> Hai...just for understanding
> loopback is configure in eBGP setup.

A Loopback interface is configured for several reasons, 
including (but not limited to) BGP.

Loopback interfaces will typically be used on eBGP setups 
for load balancing over multiple links to an upstream, or 
for eBGP multi-hop.

I tend to discourage eBGP multi-hop for a number of reasons, 
the most being it adds much unneeded complexity and 
potential for problems you'd much rather avoid.

> Loopback is virtual
> interface.. a. in configuring bgp do we need to have
> loopback

A Loopback is great for:

* iBGP sessions
* Router ID.

> b. does it using private or public ip

That doesn't matter. As long the address is routed within 
your network.

However, for commercial Internet services, recommended all 
your interfaces be numbered out of public address space, 
including your Loopback interface.

> c. in a block of IP /22 how many ip that we need to
> reserve for loopback...

Depends on how many routers you plan to have throughout your 
network.

Remember, your Loopback address takes a netmask of /32. So 
you can have as many address as you (plan to) have 
routers... with the exception of x.x.x.0 and x.x.x.255, of 
course.

Given the size of your allocation, I'd start off with a /25 
for all Loopbacks and slice it further based on how many 
routers you plan to have in each PoP. But this is your call, 
don't take my word for it :-).

> d. if i configure one interface with
> 211.1.221.3.1/30 , does the loopback using the same ip or
> others ip. TQ in advance.

No, the Loopback interface generally has its own IP address.

Cheers,

Mark.
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