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Ripv2 question (easy)

Posted on 2005-04-25
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Last Modified: 2010-04-17
This is debug output:

3w1d: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0 (192.168.2.5)
3w1d: RIP: build update entries
3w1d:   192.168.3.0/24 via 0.0.0.0, metric 1, tag 0
3w1d:   192.168.4.0/24 via 0.0.0.0, metric 1, tag 0
3w1d: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0.1 (192.168.3.1)
3w1d: RIP: build update entries
3w1d:   192.168.2.0/24 via 0.0.0.0, metric 1, tag 0
3w1d:   192.168.4.0/24 via 0.0.0.0, metric 1, tag 0
3w1d:   192.168.6.0/24 via 0.0.0.0, metric 2, tag 0
3w1d: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0.2 (192.168.4.1)
3w1d: RIP: build update entries

This is on a 2600 router w/sub interfaces obviously.
Networks attached are   192.168.2.0/28   192.168.3.0/28  and 192.168.4.0/28

1. The thing I dont understand, is the "RIP: BUILD UPDATE ENTRIES" field. What does this mean?

2. Also: 192.168.2.0, 192.168.4.0 and 192.168.6.0 do NOT have a /24 mask. Why are they showing up as /24 ???  Is this Ripv2 doing summarization?
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Question by:dissolved
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Author Comment

by:dissolved
ID: 13862962
heres a sh ip ro of the router


     192.168.4.0/28 is subnetted, 1 subnets
C       192.168.4.0 is directly connected, Ethernet0/0.2
R    192.168.6.0/24 [120/1] via 192.168.2.3, 00:00:01, Ethernet0/0
     192.168.2.0/28 is subnetted, 1 subnets
C       192.168.2.0 is directly connected, Ethernet0/0
     192.168.3.0/28 is subnetted, 1 subnets
C       192.168.3.0 is directly connected, Ethernet0/0.1
S*   0.0.0.0/0 [1/0] via 192.168.2.1
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Expert Comment

by:Don Johnston
ID: 13863484
>1. The thing I dont understand, is the "RIP: BUILD UPDATE ENTRIES" field. What does this mean?

Before the routing update can be sent, it has to be created. The routing table is parsed and an update is built.

>2. Also: 192.168.2.0, 192.168.4.0 and 192.168.6.0 do NOT have a /24 mask. Why are they showing up as /24 ???

My guess is you have "auto-summary" still enabled. RIP will automatically summerize to the classful boundary. If you want it to send the REAL mask, issue the "no auto" command from with the rip routing protocol config. (only works in Version 2 mode, though.)

-Don
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Author Comment

by:dissolved
ID: 13863498
Hi again Don:

1. so the "no auto" command stops Ripv2 from sending a classful mask. Just by issuing "no auto"  will make it start advertising the REAL mask? No other commands are needed right?

2. Does Ripv1 auto-summarize????
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Expert Comment

by:Don Johnston
ID: 13863518
Yes and no.

-Don
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Author Comment

by:dissolved
ID: 13863531
Ripv2 auto summarizes right?

Ripv1 just summarizes to whatever the default mask is. This is just it's natural behavior, it's not "auto-summary" ???
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Expert Comment

by:Don Johnston
ID: 13863538
Oops. Disregard the previous...

Yes and Yes.

-Don
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Accepted Solution

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Don Johnston earned 2000 total points
ID: 13863550
RIP v1 and v2 both auto summerize by default. With v2, you can disable summerization.

RIP v1 always summerizes to the classful boundry and you can't deiable it.

-Don
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Author Comment

by:dissolved
ID: 13863558
thanks !
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Author Comment

by:dissolved
ID: 13863612
Interesting...
I am running EIGRP and Ripv2 on this router. When EIGRP was on, all I saw was a "D."  Never say RIP.

 However, when I disabled auto-summary in my router config, RIP started showing up in my routing table. Is this normal?  Or just coincidence?


     192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks
D       192.168.4.0/24 is a summary, 01:23:29, Null0
C       192.168.4.0/28 is directly connected, Ethernet0/0.2
     192.168.6.0/24 is variably subnetted, 3 subnets, 3 masks
R       192.168.6.2/32 [120/1] via 192.168.2.3, 00:00:05, Ethernet0/0
R       192.168.6.0/30 [120/1] via 192.168.2.3, 00:00:05, Ethernet0/0
D       192.168.6.0/24 [90/2195456] via 192.168.2.3, 01:22:30, Ethernet0/0
     192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks
D       192.168.2.0/24 is a summary, 01:23:35, Null0
C       192.168.2.0/28 is directly connected, Ethernet0/0
     192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
D       192.168.3.0/24 is a summary, 01:23:35, Null0
C       192.168.3.0/28 is directly connected, Ethernet0/0.1

Before these were just all Ds and Cs
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Expert Comment

by:Don Johnston
ID: 13866750
Yes and yes.

When RIPv2 and EIGRP were running, you were learning the same /24 routes through two different routing protocols. When you learn the same network through two different protocols, administrative distance determines which get placed into the routing table. Since EIGRP has an AD or 90 and RIP is 120, the "D" routes are entered into the routing table.

When you disabled auto-summerization, the router began seeing the /28 routes. Because you hadn't disabled EIGRP's auto-summerization, those /28 routes were only being learned through RIP.

Notice though, that you're still seeing the /24 routes through EIGRP? That's because they aren't being advertised by RIP anymore.

-dj
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Author Comment

by:dissolved
ID: 13867370
So Rip is not summarizing anymore. Which is why the real masks are being shown.
EIGRP is still summarizing.

One thing I am confused about is:
>>>When you disabled auto-summerization, the router began seeing the /28 routes. Because you hadn't disabled EIGRP's auto-summerization, those /28 routes were only being learned through RIP>>>

Since EIGRP is still enabled, why didnt it take over and start routing for the /28 routes?

thanks a lot man
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Expert Comment

by:Don Johnston
ID: 13867487
> So Rip is not summarizing anymore. Which is why the real masks are being shown.

Yep

>Since EIGRP is still enabled, why didnt it take over and start routing for the /28 routes?

Because, like RIPv2, auto-summerization is enabled by default. If you disable it... Go ahead, I'll wait. Then you'll see the R routes get replaced by the D routes.

-dj
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Author Comment

by:dissolved
ID: 13871424
Thanks for help. I will play with the protocols tonight. I will post a new question I'm sure. I still do not fully understand why turning off summarization lets another routing protocol take over. ie: when I disabled Rip auto-summary, IGRP took control of some of the routes.  I dont understand what administrative distance or metric has to do with summarization I guess.

thanks again
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Expert Comment

by:Don Johnston
ID: 13871553
Admin Distance is a way of figuring out the "best" route to a network if you learn it through more than one protocol.

Put yourself in the router's position: You learn about the 172.16.0.0 network from RouterA telling you it's 3 hops away (RIP). A second or two later, you hear about from RouterB telling you it's 32456 away (IGRP). Because the two routing protocols have TOTALLY different methods of expressing "how far away" a network is, you need another method to figure out which one of these you're going to put in your routing table.

Administrative Distance...

RIP = 120 (sucks)
OSPF = 110 (Actually should be 80)
IGRP = 100 (better)
EIGRP = 90 (best)

So if you were hearing about the 172.16.0.0 network from four different routers, each one using a different protocol, the only one you'd see is the EIGRP route. Because it has the lowest AD.

-Don
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Author Comment

by:dissolved
ID: 13876557
thanks for the help Don. Rather than continue to post here, I made new questions. If you have time, can you take a look at them for me?

Thanks again

http://www.experts-exchange.com/Hardware/Routers/Q_21404334.html

http://www.experts-exchange.com/Hardware/Routers/Q_21404329.html
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