RIPng (Routing Information Protocol next generation)

You would have learnt about RIP and RIPv2. RIPng does the same thing as RIP and RIPv2. Well, almost the same thing. With few differences of course. Some of the important points are given below.

• Similar to RIP and RIPv2, RIPng is also a distance vector routing protocol which uses hop counts as a metric to determine the best path to reach  to a destination. 
• Similar to RIP and RIPv2, RIPng also has a maximum hop count of 15. One thing you need to notice here is RIP and RIPv2 uses IPv4 addressing and RIPng makes use of IPv6 addressing. Hence you would normally see that the hop count to reach a destination network will always be 1 more than what you can see in RIP and RIPv2. That's how IPv6 addressing works folks.
• RIPng also makes use of split horizon, poison reverse and similar techniques to avoid loops in a network
• RIP and RIPv2 uses UDP with port number 520 where as RIPng uses UDP port number 521
• RIPv2 uses the multicast address 229.0.0.9 for sending and receiving routing updates. RIPng uses the IPv6 multicast address FF02::9 for the same.
• RIPng does not support authentication on its own. The IPSec feature of IPv6 can be used to provide authentication for out RIPng packets. More on authentication of RIPng in another article. 
• RIPng is supported on Cisco IOS 12.2(2)T and above. 

OSPF DR-BDR Election

If a router running OSPF has to exchange routes with another router running OSPF, then a nighborship between the 2 routers is not sufficient. The 2 routers have to form am adjacency.
2 routers forming an adjacency depends on the type of network used.

In case of a BMA or an NBMA network, a DR-BDR election takes place to elect a DR(Designated Router) and a BDR(Backup Designated Router).
All other routers in the network(DROthers) will form full adjacencies with the DR and the BDR.

The topology is an example for a BMA network. Routers R1 through R5 will send and receive Hello Packets and they will form neighborship with each other. Since this is a BMA network, all these routers will not form adjacencies with each other. Routers R1 through R5 will participate in an election to elect the DR and BDR.

The Router with the highest priority will become the DR and the router with the second highest priority will become the BDR. The OSPF priority for all the routers are the same by default. The value is 1. That means R1 through R5 have the same router priority. In this case, the router ID breaks the tie. The router with the highest router ID will become the DR and the router with the second highest router ID will become the BDR. 

In the example, considering the priorities to be the default on all the routers, we can come to a conclusion that R5 is the DR and R3 is the BDR. 

R1, R2 and R4 will form neighborship with each other and also the DR and BDR but they will form adjacencies only with DR and BDR (R5 and R3). R1, R2 and R4 will exchange their LSDBDs with R5 and R3. R1, R2 and R4 will use the multicast address 224.0.0.6 to send routing updates to DR or BDR. In turn DR and BDR sends these routing updates to all other routers (DROthers) on the multicast address 224.0.0.5.

If the DR goes down, the BDR takes its place. Doing this in a BMA network reduces a lot of network traffic as the DR and BDR are considered to be the central point for update traffic.

A similar thing happens with an NBMA network also.