Well loads of answers already, but my £0.02-> Routes to null can be used to blackhole traffic with lower overhead that an ACL, but obviously with less granuality.
You could also use routes to null for redistribution, I have used this in the case of EIGRP when I wanted to redistribute static routes into EIGRP but wanted to keep them as internal routes, added a route to null and then redisitributed it that way .. static routes the specifiy an interface as the next hop are redistributed as locally connected and this internal metrics. Lastly, and what it seems to be used for in your case is BGP summarisation. Say for eg you had various /26's in your routing table, we would want to summarize this out to the rest of the world as a single /24. BGP will only advertise routes that are present in your internal routing process. This to force the BGP process to advertise the larger /24 prefix, you have to manuall inject this route into your routing table by using the route to null? Emilia Lambros wrote: > > Though to answer your question :) > > Summarization means advertising the biggest network you > choose/should advertise. If you had a /23 that was routed as 2 > /24s in your network, you'd summarize those as a /23 on the way > out of your network to keep the routing table smaller... > > You should probably do the same for your next /24 unless you > can find a specific reason not to. It saves headaches with > route dampening in the long run if nothing else :) > > > > > -----Original Message----- > From: Anil Gupte [mailto:[EMAIL PROTECTED] > Sent: Friday, 4 April 2003 7:21 AM > To: [EMAIL PROTECTED] > Subject: Re: IP route to Null0? [7:66755] > > > You are right, it is using BGP. What does summarization do? > Do I need an identical statement for my new Class C? > > Thanx, > Anil Gupte > > ----- Original Message ----- > From: "Karsten" > To: "Anil Gupte" ; > Sent: Thursday, April 03, 2003 10:46 AM > Subject: Re: IP route to Null0? [7:66755] > > > Either a sloppy way to drop traffic for a /24, or bgp > summarization using null routing. > > -Karsten > > On Thursday 03 April 2003 07:40 am, Anil Gupte wrote: > > I am trying to understand some IP route commands on our > router. Several > of > > them go to Null0 - what does that mean? > > > > For example, I have > > ip route xxx.xxx.xxx.0 255.255.255.0 Null0 200 > > > > What is this doing? > > > > I need to add another block of class Cs from the same > provider. Do I need > > a similar statement to the above? > > > > Thanx for your help. > > Anil Gupte > > Nondisclosure violations to [EMAIL PROTECTED] > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=66830&t=66755 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
