RIPv1 Questions? broadcast

lildeezul

Ok im reading lammle book, chapter 6 on ip routing. I have understanded static routes, and load balancing thanks to yall ( techexams), and learned a lesson about windows. ( cant ping routers, if you have 2 nics enabled)....

but anyway i have successfully configured ripv1 with my routers, and i can ping host to routers, and routers to other routers on different networks.
My network is as follows:
i have issued the debug ip rip. I see that my router sends a layer 3 broadcast of 255.255.255.255 meaning "All Network, ALL HOST". I understand that routers can send broadcast, but if it recieves a broadcast, it gets dropped. well according to my network if
2611-1 send the broadcast containing its known routing table to routers 2501-2, doesnt it get dropped by 2501-2, If i am right, how does 2501-1 get the information from 2611-1??

Or does this broadcast get forwarded becauase its a layer 3 broadcast meaning 'All networks all host"

confused about this. How can this mean all networks if broadcast only stay on the LAN, and doesnt go through routers.

please explain!

Thanks!

gojericho0

You are correct the 255.255.255.255 is a layer 3 broadcast and will get forwarded out all interfaces and received by all directly connected neighbors. RIP learns routing information from directly connected neighbors. Your 2501-1 will learn the route for the 2611 from its neighbor 2501.2.

Question for you. What protocol uses a layer 2 broadcast to get information on a network?

Also why isn't your 2501-1 broadcasting the 192.168.20.0 network it learned from 2501-2 out its Serial 0 interface even though a layer 3 broadcast to send routing updates

lildeezul

2501-1#sh
03:38:34: RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.30.2) -
suppressing null update
03:38:38: RIP: received v1 update from 192.168.30.1 on Serial0
03:38:38: 192.168.10.0 in 2 hops
03:38:38: 192.168.20.0 in 1 hops

---

O so i see. layer 3 broadcast will get forwarded to connected devices.
I get it know, my 2501-1 will get info about 192.168.10.0 from the 2501-2 router. and the 2501-
2 router recieved the info about 192.168.10.0 from 2611-1.

Also one more thing when dubuggin the rip protocol, my 2501-2 is sending back info about networks that i already know ( which i just sent to it)

ex:03:41:17: RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.30.2) -
suppressing null update
03:41:24: RIP: received v1 update from 192.168.30.1 on Serial0
03:41:24: 192.168.10.0 in 2 hops
03:41:24: 192.168.20.0 in 1 hops
03:41:44: RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.30.2) -
suppressing null update
03:41:50: RIP: received v1 update from 192.168.30.1 on Serial0
03:41:50: 192.168.10.0 in 2 hops
03:41:50: 192.168.20.0 in 1 hops

i can avoid this my split horizon correct. Well how do i enable it???

lildeezul

To answer that question..
Since layer 2 broadcast are representing by mac addresses, and mac addresses are only on the LAN,
I would say ARP becuase to communication on the LAN, you would use the MAC address, and if you dont know the mac an arp broadcast is issued.

Am i correct?

gojericho0

You are correct with both questions. Split horizon is enabled by default, the remote network updates you are receiving from 2501-2 will not be sent back out the 2501-1 Serial 0 interface.

APA

RIPv1 broadcasts to directly connected neighbours....... Hence you see in your diagram that the Serial interfaces between each router are sharing the same broadcast domain so the RIP routing updates are accepted.....

Remember that rach router configured with RIP only shares the it's routing table with directly connected RIP routers.... (Direct neighbours)

To enable split-horizon to prevent routing loops, enable it under the respective interfaces taking part in the RIP routing process

rip 10
network 10.10.0.0 0.0.0.255

interface fa 0/1
ip address 10.10.0.1 255.255.255.0
ip split-horizon (or no ip split-horizon)


I haven't configured RIP in a while so someone please correct me.......

You might want to consider playing with poison-reverse configs as well so when a a link goes does other routers are informed by increasing hop count to lost router to 16 (infinite - implying can't get there) as the RIP max hop count is 15...

mikej412

lildeezul wrote:

I understand that routers can send broadcast, but if it recieves a broadcast, it gets dropped. well according to my network if 2611-1 send the broadcast containing its known routing table to routers 2501-2, doesnt it get dropped by 2501-2, If i am right, how does 2501-1 get the information from 2611-1??

RIP is a "Routing by Rumor" protocol. The 2501-1 doesn't get the information from 2611-1 -- it hears about 2611-1 (and it's routes) from 2501-2.

2501-2 broadcasts it's own RIP routes out to 2501-1, and that includes the information about the existence of 2611-1 (and the routes 2611-1 told 2501-2 about).

One router is taking the other routers word that the information it is getting is correct.

lildeezul

thanks for all the clarifications guys