Hi PPL,

Need an ans for this question. 2 similar question but different answers. What are the differences in the quetion?

1)Your Ethernet network, 172.30.1.0 shuts down. which update message is seen in your router's debug ip rip output regarding that network?
A) subnet 172.30.1.0, metric 0
B) subnet 172.30.1.0, metric 1
C) subnet 172.30.1.0, metric 15
D) subnet 172.30.1.0, metric 16

Ans: C

2)Your Ethernet network, 172.30.1.2 shuts down. which update message is seen in your router's debug ip rip output regarding that network?
A) subnet 172.30.1.0, metric 0
B) subnet 172.30.1.0, metric 1
C) subnet 172.30.1.0, metric 15
D) subnet 172.30.1.0, metric 16

Ans: D

RIP
RIP is a distance vector routing protocol that uses hop count as its metric. The maximum hop count is 15 so 16 hops is deemed unreachable. RIP updates are boradcast every 30 seconds by default. RIP is enable by typing.

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Those answers are wrong.

Scenario #1: D - "16"

I attached real router output below. 16 is the RIP value of infinity, not 15.

Scenario #2: All wrong!

Subnet 172.30.1.2 is only possible with a /31 mask - and that's only allowed on point-to-point links. Not Ethernet!

Cheers,
Ron

---
Ron Steedman CCNP, CCNA, MCP, BS Computer Science
Free CCNA Practice Tests, Study Guides, & Message Boards!
http://www.congonetworking.com/


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
router(config-if)#shut
router(config-if)#
3d20h: RIP: sending v1 update to 255.255.255.255 via FastEthernet1/0 (1.1.1.1)
3d20h: network 172.30.0.0, metric 16
3d20h: RIP: sending general request on FastEthernet1/0 to 255.255.255.255
3d20h: RIP: sending general request on FastEthernet1/0 to 224.0.0.9
3d20h: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administrat
vely down
3d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed
state to down
router(config-if)#
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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A couple notes on the debug ip rip output:

1.

Cisco sends BOTH RIPv1 (broadcast) and RIPv2 (multicast) updates by default on IOS 12.0.

Note how "sending general request" is shown twice - once for 255.255.255.255 (broadcast) and once for 224.0.0.9 (multicast).

You can configure the router to send only one update with "version {1|2}".

2.

Advertising the "shutdown" route with a value of infinity is called POISON REVERSE. It lets other routers know that the route is down and helps prevent routing loops.

"16" is infinity for RIP. That's why RIP is limited to networks that are less than or equal to 15 hops in diameter.

Cheers,
Ron

---
Ron Steedman CCNP, CCNA, MCP, BS Computer Science
Free CCNA Practice Tests, Study Guides, & Message Boards!
http://www.congonetworking.com/

Last edited by rsteedma on 07-05-02 at 06:39 AM

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For Q2

Why 172.30.1.2 does not exist in eth?

There is no hint about RIPv1 or v2. If it is v1, that only default class B mask is allowed, that 255.255.0.0, i.e. route to be advertising is 172.30.0.0/16.

For CCNA q., I think if there is not specified, classful network should be assumed.

The admin. may use 30-bit netmask (not /31), only two ip addresses for two point-to-point serial links for saving addresses. There is no restriction that only use 172.30.1.1/30 in serial. It can also use in any interface with any netmask as long as these addresses are available. You may assign 172.30.1.0/16 to eth0 that all hosts from 172.30.1.1 - 172.30.255.254 includes in this large network.

Not intend to agrue with you. Just discussing.

Correct me if I am in wrong.

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pomerol82
Poor is not a sin, but the rich makes it be sin;
Rich is not supreme, but the poor wishes be supreme.

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Hello,

My doubts and thoghts:
Q# 1 and 2 states
"Ethernet network, 172.30.1.0 shuts down"
"Ethernet network, 172.30.1.2 shuts down"

My understanding:
172.30.1.0 means whole subnet is shuted
172.30.1.2 means a R's interface is shuted.

I'd consider Rsteedma's answer for the Q1 to be correct for the both Qs.

I have no router to test, but I am centred to Q1's answer Zero (A) too.


Your thoughts?
MateLom.

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Hi Pomerol,

>>>>>
Cisco only recently began to support /31 masks on point-to-point links:

"Using 31-Bit Prefixes on IPv4 Point-to-Point Links"

http://www.cisco.com/univercd/cc/td...t2/ft31addr.htm
>>>>>

It's not relevant to the CCNA exam, but it's good to know.

Cheers,
Ron

---
Ron Steedman CCNP, CCNA, MCP, BS Computer Science
Free CCNA Practice Tests, Study Guides, Message Boards!
http://www.congonetworking.com/

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Hi Razamuv,

Here's what each metric means:

0 - Invalid. Never sent by RIP.
1 - Valid - 1 Hop Away
15 - Valid - 15 Hops Away
16 - Valid - INFINITY.

From RIP's rfc (#1058):

"The metric field must contain a value between 1 and 15 inclusive, specifying the current metric for the destination, or the value 16, which indicates that the destination is not reachable."

ZERO is tricky. It's thrown in there to confuse you.

Cheers,
Ron

---
Ron Steedman CCNP, CCNA, MCP, BS Computer Science
Free CCNA Practice Tests, Study Guides, Message Boards!
http://www.congonetworking.com/

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Thanks a lot, Rsteedma !

But, is it correct to say:

172.30.1.0 means whole subnet is shuted
172.30.1.2 means a R's interface is shuted.


I'd consider your answer for the Q1 to be correct for the both Qs.

Cheers,
MateLom.

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What probably happened is that the second person made a typo copying the question from the first person.

quote:

---

Your Ethernet network, 172.30.1.2 shuts down. which update message is seen in your router's debug ip rip output regarding that network?

---

I would report this as an error to Cisco since it calls 172.30.1.2 a network. I would then pick 16 since it's "what they want".

Withdrawn routes are always 16 hops away.

quote:

---

Your Ethernet interface, 172.30.1.2 shuts down. which update message is seen in your router's debug ip rip output regarding the network?

---

I would answer "16" to this question and be happy about it.

Cheers,
Ron

---
Ron Steedman CCNP, CCNA, MCP, BS Computer Science
Free CCNA Practice Tests, Study Guides, Message Boards!
http://www.congonetworking.com/

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Respect

MateLom.

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