From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Sat Oct 28 2006 - 06:40:56 ART
Anthony,
I can add a little comment here. The thing I'd like to point out is
that your exhibit looks incomplete. First, let's take a look at
the exhibit itself:
<quote>
Exhibit 1
RouterA(config)# router eigrp 100
RouterA(config-router)# network 10.0.0.0
RouterA(config-router)# network 172.16.10.0
RouterA(config-router)# exit
RouterA(config)# ip default-network 172.16.10.0
RouterA(config)# ip route 172.16.10.0 255.255.255.0 172.16.10.1
</quote>
To begin with, "ip default-network" command is CLASSFUL.
That is, when you issue "ip default-network 172.16.10.0" IOS will
generate static route like "ip route 172.16.10.0 255.255.255.0
172.16.10.1" and will not produce a default network yet.
To produce default-network you need additional statement:
"ip default-network 172.16.0.0" to be issued.
Here is a live example :)
*Before* we configure any "ip default-network command":
-------------------------------
R3#show ip route
Codes: 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, 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 110.50.13.49 to network 0.0.0.0
<snip>
144.144.0.0/24 is subnetted, 1 subnets
O E2 144.144.144.0 [110/20] via 110.50.13.50, 00:27:37, FastEthernet0/0.5
<snip>
O*E2 0.0.0.0/0 [110/1] via 110.50.13.49, 00:27:38, FastEthernet0/0.5
-------------------
Now, we are going to make 144.144.0.0/16 a default-network. To do that, we
first issue:
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#ip default-network 144.144.144.0
Some verifications:
R3(config)#do sh run | inc ip default
None found!
R3(config)#do sh run | inc ip route
ip route 144.144.0.0 255.255.0.0 144.144.144.0
A static for CLASSFUL network has been generated pointing at
original prefix. Let's see if we have new gateway of last resort:
R3(config)#do show ip route | inc Gateway of last
Gateway of last resort is 110.50.13.49 to network 0.0.0.0
Nope, it did not change!
Now, we issue yet another commad:
R3(config)#ip default-network 144.144.0.0
A CLASSFUL variant, and verify it:
R3(config)#do show run | inc ip default
ip default-network 144.144.0.0
Check the routing table:
R3(config)#do show ip route | inc Gateway of last
Gateway of last resort is 144.144.144.0 to network 144.144.0.0
R3(config)#do show ip route | inc 144.144.0.0
Gateway of last resort is 144.144.144.0 to network 144.144.0.0
* 144.144.0.0/16 is variably subnetted, 2 subnets, 2 masks
S* 144.144.0.0/16 [1/0] via 144.144.144.0
If we want to propagate the default-network to other EIGRP routers, we
may simply redistribute generated static route into EIGRP:
conf t
router eigrp 200
redistribute static
And check the neighbor's routing table (sorry for VRFs):
SW2#show ip route vrf BACKBONE
Routing Table: BACKBONE
Codes: 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, E - EGP
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
Gateway of last resort is 150.1.0.3 to network 144.144.0.0
D*EX 144.144.0.0/16 [170/30720] via 150.1.0.3, 00:00:10, FastEthernet0/3
13.0.0.0/24 is subnetted, 2 subnets
D 13.13.13.0 [90/156160] via 150.1.0.3, 00:41:29, FastEthernet0/3
D 13.14.13.0 [90/156160] via 150.1.0.3, 00:41:29, FastEthernet0/3
150.1.0.0/24 is subnetted, 1 subnets
C 150.1.0.0 is directly connected, FastEthernet0/3
Finally, thanks a lot for an interesting question! Default-network
is confusing topic for many of us :)
HTH
2006/10/28, anthony.sequeira@thomson.com <anthony.sequeira@thomson.com>:
>
> Congrats to Bajo [bajoalex@gmail.com] for winning the Cisco Press title
> last
> week!
>
> We will randomly draw again this week from the responses sent to
> anthony.sequeira@thomson.com. The winner will receive the CCIE Routing
> and Switching Flash Cards and Exam Practice Pack from Cisco Press.
>
> REMEMBER:
>
> All questions will be carefully selected to have CCIE Lab relevance as
> well as relevance to the written exam!
>
> LAST WEEK'S RESPONSES:
>
> A - 40%
> B - 20%
> C - 40%
> D - 0%
>
> LAST WEEK'S ANSWER:
>
> Answer: a, b, c
>
> Topic Domain: 4c
>
> Issue:
> How is the ip default-network used in conjunction with EIGRP?
>
> Solution:
> The network specified by the ip default-network command must be
> reachable by the router that uses this command before it announces it as
> a candidate default route to other EIGRP routers. The network specified
> by this command must also be passed to other EIGRP routers so that those
> routers can use this network as their default network and set the
> gateway of last resort to this default network. The local router will
> not show a gateway of last resort set - neighboring routers will show
> this value as set. Multiple default networks can be configured -
> neighboring routers use the EIGRP metric to determine the best default
> route.
>
> More Information:
> Configuring a Gateway of Last Resort Using IP Commands
> http://www.cisco.com/warp/public/105/default.html
>
>
> LAST WEEK'S QUESTION:
>
> 4-5-8. Examine the configuration shown in Exhibit 1. Which statements
> regarding this configuration are true? Choose all that apply.
>
> a. For EIGRP to propagate the default route, the network specified
> by the ip default-network command must be known to EIGRP
>
> b. RouterA will not show a gateway of last resort set in the show
> ip route output
>
> c. The network specified by the ip default-network command must be
> passed to other EIGRP routers
>
> d. Multiple default networks cannot be configured
>
> Exhibit 1
> RouterA(config)# router eigrp 100
> RouterA(config-router)# network 10.0.0.0
> RouterA(config-router)# network 172.16.10.0
> RouterA(config-router)# exit
> RouterA(config)# ip default-network 172.16.10.0
> RouterA(config)# ip route 172.16.10.0 255.255.255.0 172.16.10.1
>
>
> THIS WEEK'S QUESTION:
>
> 2-5-2. Examine the Catalyst switch output shown in Exhibit 1. What
> version of STP is in use on this switch?
>
> a. 802.1d
> b. 802.1w
> c. 802.1s
> d. 802.1q
>
> Exhibit 1
> ASW1#show spanning-tree vlan 1
>
> VLAN0001
> Spanning tree enabled protocol ieee
> Root ID Priority 32769
> Address 000d.28c6.6800
> Cost 19
> Port 2 (FastEthernet0/2)
> Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
>
> Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
> Address 000d.2903.8980
> Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
> Aging Time 300
>
> Interface Role Sts Cost Prio.Nbr Type
> ---------------- ---- --- --------- --------
> --------------------------------
> Fa0/1 Altn BLK 19 128.1 P2p
> Fa0/2 Root FWD 19 128.2 P2p
>
>
> Question of the Week Compliments of:
>
> TESTiT
> http://www.netmasterclass.com/site/written.php
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
-- Petr Lapukhov, CCIE #16379 petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com Toll Free: 877-224-8987 Outside US: 775-826-4344
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