Solved: router summarization - in RIP - does it work ?

SJ K · ‎05-08-2015

Hi all,

Below is my network topology and i am trying to see how to simulate route summarization

When doing a show ip protocols on Router5 , this is what i see (network summarization in effect)

Router#show ip protocols
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 23 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Redistributing: rip
Default version control: send version 1, receive any version
  Interface             Send  Recv  Triggered RIP  Key-chain
  FastEthernet0/0       1     2 1   
  FastEthernet0/1       1     2 1   
Automatic network summarization is in effect
Maximum path: 4
Routing for Networks:
    192.168.3.0
    192.168.4.0
Passive Interface(s):
Routing Information Sources:
    Gateway         Distance      Last Update
    192.168.3.1          120      00:00:12
Distance: (default is 120)
Router#

So i am thinking when advertising to the next Router8, Router 5 will send it as 192.168.0.0/22 which covers 192.168.0.0 to 192.168.3.255.

But on Router 8, I do a show ip route, it isn't reflecting a summary route.

============

q1) route summarization is done in the sending routers via route advertisements itself or after receiving route advertisements in the receiving router ?

q2) is it because i am running RIP that why the route summarization don't work ; as RIP does not support CIDR. But then, what does the Route summarization highlighted in red above means ?

Do I have to summarize in classful boundaries ? that means i can have subnets (e.g. 192.168.0.0/25 and 192.168.0.128/25) and the router will send it as 192.168.0.0/24 ?

Please advise.

Regards,
Noob

Mark Malone · ‎05-08-2015

You dont have to but in real world you would otherwise RIP will summarize your routes into a classful network , if you have multiple subnets /26,/29 etc RIP will summarize all these into the major classful network which is not ideal in real world

To prevent this happening you use ripv2 and the no auto summary this will allow you to see all your specific routes in the routing table , then by choice if you want you can manually summarize them on an interface to whatever you decide and this summarized route will be passed upstream , if you dont use the no auto-summary you will only see classful subnets as ripv1 does this by default as its not smart enough to deal with classless but ripv2 is.

View solution in original post

Jon Marshall · ‎05-08-2015

I have recieved routes from 192.168.0.0 to 192.168.3.0 from another R1. But R1 does not summarize them to 192.168.0.0/22.

No routing protocol will summarise that range unless you tell it to.

It doesn't matter whether auto summarisation is off or on.

That summary range is a classless summary and routers only perform automatic summarisation on classful boundaries.

There is no such thing as auto summarisation for classless ranges like the above because the routing protocol has no way of knowing that is the summary address you want advertised.

If you want to advertise that summary address you have to do it manually ie. under the interface you want the summary address to be advertised out of -

int <x/y>
ip summary-address rip 192.168.0.0 255.255.252.0

Jon

View solution in original post

Mark Malone · ‎05-08-2015

Route summarization is done by the router doing the actual task it needs to be specified , the part in RED means usually you have not got no auto-summary enabled , if add the no auto summary under the process it will change to automatic summarization is not in effect

Ripv1 is classful while Ripv2 is classless , real summarization for RIP is performed under the interface rather than the protocol process like ospf , eigrp works the same as there both distance vector based

ip summary-address rip x.x.x.x x.x.x.x

This shows working example

http://www.freeccnaworkbook.com/workbooks/ccna/configuring-rip-route-summarization

SJ K · ‎05-08-2015

Hi Mark,

the part in RED means usually you have not got no auto-summary enabled , if add the no auto summary under the process it will change to automatic summarization is not in effect

Sorry my english is not very good. Do you mean that the part in red means auto-summarization is on ?

Ripv1 is classful while Ripv2 is classless , real summarization for RIP is performed under the interface

Do you mean that the RIP route summarization is done on the sender's interface ?

Lastly, why isn't my setup above doing auto-summarization from router 5 to 6 ?

Regards,
Noob

Mark Malone · ‎05-08-2015

yes summarization is on by default for classful network , thats the way its set out of the box for RIP, the result your trying to get is not classful its a /22 classless subnet it works the other way around with RIP by default it summarizes to the classful networks , classful subnets are /8 , /16 /24 255.0.0.0,255.255.0.0,255.255.255.0

With RIP if you want to see the results your expecting you need to use RIPv2 and turn on no auto-summary under the process , create multiple loopbacks on 1 of the routers advertise them and then summarize them at interface level using the ip summary-address statement then on your upstream router you will see the summarized route in the routing table

Its more striaght forward with eigrp as its classless from the start

SJ K · ‎05-08-2015

Hi Mark,

Thanks for replying.

With RIP if you want to see the results your expecting you need to use RIPv2 and turn on no auto-summary under the process , create multiple loopbacks on 1 of the routers advertise them and then summarize them at interface level using the ip summary-address statemen then on your upstream router you will see the summarized route in the routing table

Why do we have to turn on "no auto-summary" when we are expecting auto-summary ?

Regards,
Noob

Mark Malone · ‎05-08-2015

You dont have to but in real world you would otherwise RIP will summarize your routes into a classful network , if you have multiple subnets /26,/29 etc RIP will summarize all these into the major classful network which is not ideal in real world

To prevent this happening you use ripv2 and the no auto summary this will allow you to see all your specific routes in the routing table , then by choice if you want you can manually summarize them on an interface to whatever you decide and this summarized route will be passed upstream , if you dont use the no auto-summary you will only see classful subnets as ripv1 does this by default as its not smart enough to deal with classless but ripv2 is.

SJ K · ‎05-08-2015

Hi Mark,

Does RIPV2 (as a classless protocol) with auto-summary on still summarized routes in to "Classful" boundaries ?

Regards,
Noob

Mark Malone · ‎05-08-2015

I have not tested that always use the no auto-summary but i would say yes it would still summarize to classful , i know eigrp does summarize to classful without it so i would persume ripv2 is the same , even though its capable of being classless unlike version 1 you have the option to tell it not to be classful , that and the fact version2 multicasts the routing table to its neighbours instead of broadcasting it are the some of the main differences , subnets are advertised in version2 as well

SJ K · ‎05-08-2015

Hi Mark,

Seems like auto-summary still summarize to classful boundaries in RIPV2

RIP: received v2 update from 192.168.4.1 on FastEthernet0/0
      192.168.0.0/24 via 0.0.0.0 in 1 hops
      192.168.1.0/24 via 0.0.0.0 in 1 hops
      192.168.2.0/24 via 0.0.0.0 in 1 hops
      192.168.3.0/24 via 0.0.0.0 in 1 hops

Router#
Router#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

R    192.168.0.0/24 [120/1] via 192.168.4.1, 00:00:11, FastEthernet0/0
R    192.168.1.0/24 [120/1] via 192.168.4.1, 00:00:11, FastEthernet0/0
R    192.168.2.0/24 [120/1] via 192.168.4.1, 00:00:11, FastEthernet0/0
R    192.168.3.0/24 [120/1] via 192.168.4.1, 00:00:11, FastEthernet0/0
C    192.168.4.0/24 is directly connected, FastEthernet0/0

R1 <--> Router

I have recieved routes from 192.168.0.0 to 192.168.3.0 from another R1. But R1 does not summarize them to 192.168.0.0/22.

Not sure if it is a bug in packet tracer or it is really the correct behaviour.

Regards,
Noob

Jon Marshall · ‎05-08-2015

I have recieved routes from 192.168.0.0 to 192.168.3.0 from another R1. But R1 does not summarize them to 192.168.0.0/22.

No routing protocol will summarise that range unless you tell it to.

It doesn't matter whether auto summarisation is off or on.

That summary range is a classless summary and routers only perform automatic summarisation on classful boundaries.

There is no such thing as auto summarisation for classless ranges like the above because the routing protocol has no way of knowing that is the summary address you want advertised.

If you want to advertise that summary address you have to do it manually ie. under the interface you want the summary address to be advertised out of -

int <x/y>
ip summary-address rip 192.168.0.0 255.255.252.0

Jon

SJ K · ‎05-08-2015

Hi Jon,

Nice to hear from you again. Good Friday.

Thanks for the confirmation :)

Notice the little star next to my nick ;] I have a small one like you guys too :P

Regards,
Noob

Bilal Nawaz · ‎05-08-2015

Maybe this point is covered already in the discussion, but if i've missed it, then my sincere apologies. When a classful network is participating in the routing process with classless addressing, in the same classful boundary then summarisation (be it auto or not) will not summarise. I guess it's kind of obvious, but when I first started learning networking, it took time for me to understand.

e.g.

So what I'm trying to say here is that for the 10.0.0.0/8 network, I will only see that on R4 - nowhere else, since R1, R2 and R3 have classless addressing in a classful boundary.

R4#sh ip route rip

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route

+ - replicated route, % - next hop override

Gateway of last resort is not set

R 10.0.0.0/8 [120/1] via 192.168.0.3, 00:00:17, Ethernet0/0

R3#show ip route rip

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route

+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks

R 10.1.2.0/24 [120/1] via 10.2.3.2, 00:00:11, Ethernet0/1

R2#show ip route rip

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route

+ - replicated route, % - next hop override

Gateway of last resort is not set

R 192.168.0.0/24 [120/1] via 10.2.3.3, 00:00:09, Ethernet0/1

R1#show ip route rip

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route

+ - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks

R 10.2.3.0/24 [120/1] via 10.1.2.2, 00:00:24, Ethernet0/0

R 192.168.0.0/24 [120/2] via 10.1.2.2, 00:00:24, Ethernet0/0

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

SJ K · ‎05-11-2015

Hi Bilal,

Duly noted. Thank you so much. There is no need for apologizing at all. I appreciate your advices.

I tried and yes, if the transmitting interface belongs to another classful network, then route summarization will take place.

Thanks again.