Wednesday, March 28, 2007

CCIE Routing Protocols and Multicast Notes Reminder

As I have encountered lately with numerous questions regarding Routing Protocols using multicast I have some reminder notes: 1 ) Multicast is a destination Address, mean you will never see it in the SA of a Packet. 2) Routing Protocols Such as RIPv2 , OSPF , EIGRP use multicast by default although you can set them to other then the neture behavior 3) RIPv2 224.0.0.9 / OSPF 224.0.0.5 (All OSPF Router) 224.0.0.6 (All DR/BDR) EIGRP 224.0.0.10 4) Address range 224.0.0.1 - 224.0.0.254 are non routeable address, and you ask your self how can a routing protocol use a non routable address or what is non routeable address A) non-routeable address is when a packet is living one router and reaching his nexthop router the next hop will not send it further but he will recreate another packet if he need to update others B) So when we understand what is non-routeable address we hopefully understand why a routing protocol do not need a routeable address, as you send an update you know only your next hope (or as i call it your continues address) and you cant know what is beoned that unless you get an update on that. C) what brings us to another important rule the router that get the update never send back the same update trough the same interface he received it, and this is as you know preventing routing loops or as we call it "SPLIT HORIZON" 5) also regarding continues networks in addition to all the above if you want to form a neighbor relation with another router, in addition to the specific rules of each protocol, you must be either connected directly (same subnet) or make the router think you are directly connected (by using a tunnel interface). and why you ask because of the simple fact that if I don't know how to get to you in the first place how can i make a neighbor relation as you know we are talking about IGP internal routing protocols and not BGP that you can use the multi hop (but that's for another article). I hope this has been some interesting and helpful information.
Post a Comment