In the event that you are running an internal dynamic routing protocol that would normally be the reason why the /24 is in your routing table (hence the ability for it to be in the BGP advertisements), should the place you are dynamically routing it to go away, so does your route in the IGP, thus so does the BGP route.
Since providers dampen routes that flap constantly (to avoid their own routers being bogged down by BGP), if you have problems in your internal network, it is seen by other people. If your route gets dampened, certain parts of the internet can't get to you depending on who's done the dampening. (ie, if a route flaps, the router takes notice of how many times its flapped and when it hits a threshold, the route is removed from that provider's routing table for a specified period of time, usually depending on the size of network .. small /24's go for a long time because they're usually smaller outfits, /16 goes for a short period of time because its usually going to be a bigger outfit/tier 1). A route to null0 with a high AD provides a way for that route to exist in your IGP statically should your dynamic protocol have issues. You will never lose a route to Null0 unless you add it .. remove it .. add it .. remove it .. etc :) Or your router's having serious rebooting problems .. On the other hand, you'd also lose the route if it was a directly connected interface that went down. Null0 route would also help there I'd guess. -----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=66816&t=66755 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
