Prefixes

[maher]

Hi there,

Normally, we used the prefix term to highlight how many routes/networks are installed in the routing table, how many prefix are going to advertised and so forth.If we look at sh ip bgp summary:

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

x.x.x.x 4 100 37507 15104 179941 0 0 1w3d 8404

x.x.x.x 4 100 37567 15104 179941 0 0 1w3d 8404

we know that there is 8404 prefixes available. What I'm confuse it that, does the prefixes include WAN/LAN ip networks for each routers/customers? What does it mean when somebody ask how many prefix right now?..how many prefix does your customers?...perhaps different perspective.

thanks in advance.

maher

[Harold Ritter]

Maher,

In the context of this output, it simply means the number of prefixes advertised by each neighbor. These prefixes can be anything belonging to the customer or possibly to one of their customers. You can limit this number using the "neighbor maximum-prefixes" command. Does this answer your question?

Hope this helps,

[ruwhite]

Technically, a prefix is a block of ip addresses, while a route is a block of ip addresses with a specific set of attributes, such as a next hop, communities, and etc. For instance, 10.1.1.0/24 is a prefix, while 10.1.1.0/24 with a next hop of 10.1.2.1 is a route, if that makes sense.

I think we tend to use the terms interchangably, though, which leads to a great deal of confusion, even in router show command outputs. We do this a lot, for instance, EIGRP doesn't do nonstop forwarding, it does graceful restart, but the commands are all "nsf."

:-)

Russ.W

[maher]

Hi ruwhite,

Yeah.I do agree bout that.Normally we refer the prefix to block of ip addresses.Let's assume that if I want to know how many prefixes received from my upstreams, sh ip bgp summ under the state/pfxrcd will show the output.Just wondering how the routers calculate the prefixes and summurize to the shown command.

thanks in advance.

maher

[maher]

Hi Hritter,

Thanks for the clarification.I am confused that most of of are referring to prefix and someone did ask me regarding what is prefixes? We usually used to terms referring like 203.223.122.0/18 and etc and not sure this include the service providers addressing or customers addressing..anyway,thanks for the input.

regards,

maher