Regarding ASs and Routing protocols

[Ahmed Malik]

Hi,

i have 2 questions that i want to ask.

First is that suppose in an internetwork we are running EIGRP as our routing protocol and some of the routers are running with AS 10 and some are running with AS 15. Now how will the routers from these 2 ASs will be able to communicate with each other?

Secondly, in the same network we have some routers running on Rip, some on EIGRP and some on OSPF. now is there a way for routers running on different protocols to communicate with each other?

Regards,

Ahmed

[cadet alain]

Hi,

1) you'll have to redistribute between the 2 EIGRP ASes

2) redistribution: a router running multiple routing protocols can redistribute routes from one protocol into the other

   you can do 2-way redistribution or one-way redistribution.

Post your topology and configs and we'll tell you the possible ways of achieving this along with the IOS commands.

Regards.

Alain.

[Ahmed Malik]

ok here is the topology. for question 1 consider that upper most 2 routers are running on Eigrp 10, middle 2 on eigrp 15 and bottom 2 on eigrp 18.

For question 2, consider upper 2 on eigrp, middle 2 on rip and lower 2 on ospf.

P.s... Do keep in mind that i have a dhcp server that allocates ips to all the pcs and a dns server too.

[cadet alain]

Hi,

1) so R1 is the redistribution router and under each EIGRP process you can redistribute the other ones

  eg for redistributing  EIGRP 18 in 10 and vice versa( 2 way redistribution)

  router eigrp 10

   redistribute eigrp 18 metric x x x x x

router eigrp 18

  redistribute eigrp 10 metric x x x x x

2) same redistribution point

   router rip

    redistribute ospf metric x

    redistribute eigrp x metric x

  router eigrp x

   redistribute ospf metric x x x x x

   redistribute rip metric x x x x x

router ospf x

  redistribute rip subnets

  redistribute eigrp x subnets

Alain.

[Ahmed Malik]

hi,

   this might seem a stupid question but what does "metric x.x.x.x" mean . i am asking this because i havent done redistribution yet and i simply dont know what it means. so......

Regards,

Ahmed

[cadet alain]

Hi,

all routing protocols use a different way of calculating the metric( the cost of the path to the prefix) and when multiple longest matches are coming from same protocol then the lowest metric wins and is inserted in the routing table.

As each protocol speaks a different language( hop count of RIP, composite metric of EIGRP, cost of OSPF) then you must translate from one to the other and to do this on the redistribution point you must set the seed metric.

You can do it in 2 ways:

- default-metric command under routing process where you are redistributing others

- the metric keyword in the redistribute command in the same place

The second way will always override the first one.

Now there are default seed metrics but EIGRP and RIP have a default of infinite so if you don't specify one the prefixes won't get redistributed into EIGRP or RIP.

Regards.

Alain.

[Ahmed Malik]

hi,

how will i use default metric command? and can i use any value for the metric cos it wants me to specify a value. secondly how do we determine a redistribution router or it can be anyone according to the topology design?

[cadet alain]

Hi,

for RIP: it is a hop count so eg default-metric 2

for EIGRP you must enter a 5tuple : bandwidth delay reliability load MTU

where bandwidth  is in kbps  and delay  is in tens of micro seconds so eg default-metric 1 1 1 1 1

for OSPF it is a cost so eg default-metric 15

The redistribution router is the router running all the routing processes you want to redistribute.

Regards.

Alain.