CCIE Pursuit Blog

January 27, 2008

Internetwork Expert Volume III: Lab 4 – Section 4

Interior Gateway Routing – 27 Points

4.1 Bridging

“Disable ip routing on r6”

r6(config)#no ip routing

“Bridge IP between the Frame Relay and Ethernet segments on r6”

That explains why fa0/0 does not have an IP address configured. ūüôā

After this task, I can finally ping bb1:


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5),
round-trip min/avg/max = 100/286/1032 ms

4.2 Bridging

This task confused the crap out of me.  My bridging skills are pretty poor.

“Configure the IP address of on r6.”

Ummmm….that’s already configured as the IP address of the Frame connection to bb1.¬† I guess that we’re going to use the same IP address for fa0/0 as well.

“r6 should have reachability to any address of the subnet.”
“Don’t use IRB for this task.”

No IRB.¬† CRB?¬† Actually, the IE solution doesn’t use IRB or CRB.¬† The last two subtasks are basically red herrings.¬† I will need to review bridging.

r6#sh bridge 1 group

Bridge Group 1 is running the IEEE compatible Spanning Tree protocol

   Port 4 (FastEthernet0/0) of bridge group 1 is forwarding
   Port 11 (Serial0/0.1 Frame Relay) of bridge group 1 is forwarding

r6#sh ip int br | i
FastEthernet0/0         YES manual up                    up
Serial0/0.1             YES manual up                    up


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5),
round-trip min/avg/max = 48/89/100 ms


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 0 percent (0/5)

I can’t ping r4 but I can ping bb1.¬† This poster has the opposite problem:

Task 4.2 can not ping

r6#sh cdp neigh
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
                  S РSwitch, H РHost, I РIGMP, r РRepeater

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
BB1              Ser 0/0.1          147       R T S I     2821      Ser 0/0/0:0.401
sw2              Fas 0/0            174         S I       WS-C3560- Fas 0/6

sw2#sh run int fa0/6
interface FastEthernet0/6 <-that’s a minimal configuration ūüôā

How did I miss this?????¬† Because the port on r6 was initially shut down so I didn’t see it with “show cdp neighbor” on sw2.¬† Arrgh!!!¬† I need vlan 46 assigned to this port.

sw2(config)#int fa0/6
sw2(config-if)#swit acc vl 46


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:

I guess that I can take solace in the fact that I was able to find my mistake.  I just barely missed going down a deep rabbit hole chasing bridging options.

4.3 RIPv2

I initially thought that there was an error in the IE lab because although r6 was shown as running RIP on the protocol diagram, there was no mention of r6 in the task.¬† That’s because r6 is bridging the network.¬† I turned off ip routing in task 4.1 so I wouldn’t be able to configure RIP on r6:

r6(config)#router rip
IP routing not enabled

This means that we should be able to see the routes from bb1( on r4:

r4#sh ip route rip | i
R [120/1] via, 00:00:12, FastEthernet0/0
R [120/1] via, 00:00:12, FastEthernet0/0
R [120/1] via, 00:00:12, FastEthernet0/0
R [120/1] via, 00:00:12, FastEthernet0/0

4.4 Network Redundancy

backup interface

Hmmmm….this is the reason for the point-to-point subinterface on r4 back in task 3.2

r4#sh ip int br | i Serial
Serial0/0                  unassigned      YES NVRAM  up                    up
Serial0/0.1                unassigned      YES unset  up                    up
Serial0/1              YES NVRAM  standby mode          down

r4#sh backup
Primary Interface   Secondary Interface   Status
—————–¬†¬† ——————-¬†¬† ——
Serial0/0.1         Serial0/1             normal operation



4.6  OSPF

“Use the OSPF network type that was specifically designed to handle issues with routers on the same logical IP subnet not having direct communication with each other.”

Remember that we have a multipoint subinterface on the hub (r3) and point-to-point subinterfaces on the hubs (r1 and r2).  The task calls for the point-to-multipoint OSPF network type.

r3#sh ip os nei

Neighbor ID     Pri   State           Dead Time   Address         Interface¬†¬†¬†¬†¬†¬†¬†¬† 0¬†¬† FULL/¬† –¬†¬†¬†¬†¬†¬†¬† 00:01:49¬†¬†¬†¬†¬†¬†¬† Serial0/0:0.1¬†¬†¬†¬†¬†¬†¬†¬† 0¬†¬† FULL/¬† –¬†¬†¬†¬†¬†¬†¬† 00:01:54¬†¬†¬†¬†¬†¬†¬† Serial0/0:0.1

r3#sh ip route os is variably subnetted, 5 subnets, 2 masks
O [110/65] via, 00:00:07, Serial0/0:0.1
O [110/65] via, 00:00:07, Serial0/0:0.1

4.7 OSPF


4.8 OSPF

In this task you need to advertise the loopbacks on r1 and r2 into area 0.  But r1 and r2 are not in area 0.  Time for a couple of virtual circuits.

4.9 OSPF Loopback Advertisement

“Advertise the Loopback0 networks of r3 and sw1 into OSPF.”
“These networks should appear in each other routing tables as intra-area routes.”

Since I’m not told which area to advertise the loopbacks into, can’t I just make this simple by advertising both loopbacks into area 37?¬† Answer: YES!

sw1#sh ip route | i 150.1.3.
O [110/2] via, 00:00:37, Vlan37

r3#sh ip route | i 150.1.7.
O [110/2] via, 00:00:00, FastEthernet0/0

4.10 IGP Redistribution

Four points of mutual redistribution.¬† Ugh.¬† The first two points are no worry (discontiguous RIP).¬† The other two are dangerous though.¬† I’ll work on those in task 4.11

4.11 Redistribution Loop Prevention

“Ensure that EIGRP extenal routes that are redistributed into OSPF on r1 and r2 do not get redistributed back into EIGRP.”
“Use AD to accomplish this.”

Here is a (simplified) view of the the two network redistribution points on r1 and r2:
If we do mutual redistribution between EIGRP and OSPF on r1 and r2 we’re going to have problems with D EX routes (AD of 170) being reflected back into the EIGRP domain.¬† We’re given the method for preventing this.

I missed an issue on sw1 though:

Task 4.11 Redist Loop Prevention

You need to change the RIP distance or SW1 sees the routes learnt from BB3 as OSPF external routes which it uses over the correct RIP routes. if you check the routing table on SW1, the next hop for all the BB3 subnets is R3. This is resolved by changing the AD [router rip – distance 109].



  1. I have a question here. As where i was using Dynamips and work on Internetwrk Expert workbook DYN-Lab, I observed that Distance command under rip changed AD only for the redistributed routes into RIP, (external to RIP. in other words, distance command only affect routes came by rediastribute command but not that originated by rip

    Comment by Hassan — May 26, 2008 @ 3:40 am | Reply

  2. Yes Hassan,
    I agreee with you……
    Distance command will affect the default Administrative Distance of RIP Originated Routes.

    I believe we can define metric for redistributed routes in RIP.

    Rack1R5(config-router)#redistribute eigrp 10 metric ?
    Default metric
    transparent Transparently redistribute metric


    Comment by Kaushal — December 28, 2008 @ 3:00 am | Reply

  3. Sorry Looks like little mistake….

    Router configuration commands:
    address-family Enter Address Family command mode
    auto-summary Enable automatic network number summarization
    default Set a command to its defaults
    default-information Control distribution of default information
    default-metric Set metric of redistributed routes
    distance Define an administrative distance

    One more interesting way –

    default-metric — But this will affect all redistribution that occur on the same router.
    For Example…..If we are redistributing more than one protocol in RIP for ex.. eigrp and ospf

    So the best way to achieve results depends on the task requirement.

    Comment by Kaushal — December 28, 2008 @ 3:05 am | Reply

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