📄 ip unnumbered.htm
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Sending 5, 100-byte ICMP Echos to 171.68.178.196, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms </pre>
<p><b>Conclusion:</b> The major net information is maintained
across the unnumbered point-to- point link. </p>
<h3>CASE 3</h3>
<p>On one side of the serial link we have a major net with a
subnet, and on the other side a major net with no subnet. </p>
<pre>
| |
| ---------- ---------- |
| M/S1| |S4/3 | |K/NS |
| | 7000 |----- | 2500 | |
|------| | / S0| |-------|
| E3/0| 10.2(1)| -----| 9.14(4)|E0 |
| | | | | |
| ---------- ---------- |
| |
171.68.178.196 172.68.1.1
255.255.255.192 255.255.0.0
</pre>
<p>M/S1 -- Major net M subnet 1. K/NS -- Major net K with no
subnet. </p>
<p><b>7000 Configuration:</b> </p>
<pre>
interface Ethernet3/0
ip address 171.68.178.196 255.255.255.192</pre>
<pre> interface Serial4/3
ip unnumbered Ethernet3/0 </pre>
<pre> router igrp 10
network 171.68.0.0 </pre>
<p><b>2500 Configuration:</b> </p>
<pre>
interface Ethernet 0
ip address 172.68.1.1 255.255.0.0</pre>
<pre> interface Serial 0
ip unnumbered Ethernet0 </pre>
<pre> router igrp 10
network 172.68.0.0 </pre>
<p><b>7000 Results:</b> </p>
<pre>
FRCS7-2# sh ip route 172.68.0.0
Routing entry for 172.68.0.0 (mask 255.255.0.0)
Known via "igrp 10", distance 100, metric 8576
Redistributing via igrp 10
Advertised by igrp 10
Last update from 172.68.1.1 on Serial4/3, 00:00:58 ago
Routing Descriptor Blocks:
* 172.68.1.1, from 172.68.1.1, 00:00:58 ago, via Serial4/3
Route metric is 8576, traffic share count is 1
Total delay is 21000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 128/255, minimum MTU 1500 bytes
Loading 1/255, Hops 0
</pre>
<pre> FRCS7-2#ping 172.68.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.68.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5) </pre>
<p><b>2500 Results:</b> </p>
<pre>
FRCS251-1#sh ip route 171.68.0.0</pre>
<pre> Routing entry for 171.68.0.0 (mask 255.255.255.255), 49 known subnets
Known via "igrp 10", distance 100, metric 8786
Tag 0
Redistributing via igrp 10
Last update from 171.68.178.196 on Serial0, 00:00:36 seconds ago </pre>
<pre> I 171.68.174.64 [100/8786] via 171.68.178.196, 0:00:36, Serial0
I 171.68.170.64 [100/8786] via 171.68.178.196, 0:00:36, Serial0
I 171.68.231.0 [100/8806] via 171.68.178.196, 0:00:36, Serial0
I 171.68.230.0 [100/8806] via 171.68.178.196, 0:00:36, Serial0
I 171.68.187.64 [100/8696] via 171.68.178.196, 0:00:36, Serial0
I 171.68.159.64 [100/9696] via 171.68.178.196, 0:00:36, Serial0
I 171.68.158.64 [100/9696] via 171.68.178.196, 0:00:36, Serial0 </pre>
<p>As we see here, the 7000 has sent updates containing its
subnets but the 2500 does not expect to see subnets in the
updates it receives. As a result, the 2500 marks the updates as
being learned with a subnet mask of 255.255.255.255, which makes
the subnets look like host routes. Since there is no route for
171.68.178.196, the following ping won't work: </p>
<pre>
S251-1#ping 171.68.178.196
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 171.68.178.196, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
</pre>
<p><b>Solution:</b> The 7000 knows how to reach the network
172.68.0.0, but the 2500 has lost that information by treating
the subnet updates as host routes. A static route in the 2500
like ip route 171.68.0.0 s 0 will do the trick. </p>
<pre>
FRCS251-1#sh ip route 171.68.0.0</pre>
<pre> Routing entry for 171.68.0.0 (mask 255.255.0.0), 50 known subnets
Attached (1 connections) Variably subnetted with 2 masks
Known via "igrp 10", distance 100, metric 8786 (connected)
Tag 0
Redistributing via igrp 10
Last update from 171.68.178.196 on Serial0, 0:00:26 seconds ago </pre>
<pre> S 171.68.0.0 is directly connected, Serial0
I 171.68.174.64 255.255.255.255 [100/8786] via 171.68.178.196, 0:00:26, Serial0
I 171.68.170.64 255.255.255.255 [100/8786] via 171.68.178.196, 0:00:26, Serial0 </pre>
<pre> FRCS251-1#ping 171.68.178.196
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 171.68.178.196, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms </pre>
<p><b>Conclusion:</b> The subnet information gets lost since it
is treated as a host route. Add the static route to fix this. </p>
<h3>CASE 4</h3>
<p>On both sides of the serial link we have two different major
nets with respective subnets. </p>
<pre>
| |
| ---------- ---------- |
| M/S1| |S4/3 | |K/S1 |
| | 7000 |----- | 2500 | |
|------| | / S0| |-------|
| E3/0| 10.2(1)| -----| 9.14(4)|E0 |
| | | | | |
| ---------- ---------- |
| |
171.68.178.196 172.68.1.1
255.255.255.192 255.255.255.192
</pre>
<p>M/S1 -- Major net M subnet 1. K/S1 -- Major net K subnet 1. </p>
<p><b>7000 Configuration:</b> </p>
<pre>
interface Ethernet3/0
ip address 171.68.178.196 255.255.255.192</pre>
<pre> interface Serial4/3
ip unnumbered Ethernet3/0 </pre>
<pre> router igrp 10
network 171.68.0.0 </pre>
<p><b>2500 Configuration:</b> </p>
<pre>
interface Ethernet 0
ip address 172.68.1.1 255.255.255.192</pre>
<pre> interface Serial 0
ip unnumbered Ethernet0 </pre>
<pre> router igrp 10
network 172.68.0.0 </pre>
<p><b>7000 Results:</b> </p>
<pre>
FRCS7-2#sh ip route 172.68.0.0
Routing entry for 172.68.0.0 (mask 255.255.255.255),
Redistributing via igrp 10
Advertised by igrp 10</pre>
<pre> I 172.68.254.0 255.255.255.255 [100/8576] via 172.68.1.1, 00:01:06, Serial4/3
I 172.68.1.0 255.255.255.255 [100/8576] via 172.68.1.1, 00:01:06, Serial4/3 </pre>
<pre> FRCS7-2#ping 172.68.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.68.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5) </pre>
<p><b>2500 Results:</b> </p>
<pre>
FRCS251-1#sh ip route 171.68.0.0
Routing entry for 171.68.0.0 (mask 255.255.255.255), 50 known subnets
Known via "igrp 10", distance 100, metric 8786
Tag 0
Redistributing via igrp 10
Last update from 171.68.178.196 on Serial0, 0:01:17 seconds ago</pre>
<pre> I 171.68.178.192 [100/8786] via 171.68.178.196, 0:01:17, Serial0
I 171.68.174.64 [100/8786] via 171.68.178.196, 0:01:17, Serial0
I 171.68.170.64 [100/8786] via 171.68.178.196, 0:01:17, Serial0
I 171.68.231.0 [100/8806] via 171.68.178.196, 0:01:17, Serial0
I 171.68.230.0 [100/8806] via 171.68.178.196, 0:01:17, Serial0 .... </pre>
<pre> FRCS251-1# ping 171.68.178.196
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 171.68.178.196, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5) </pre>
<p><b>Solution:</b> This is an extension of Case 3. To solve this
we apply static routes to both ends of the serial link: </p>
<p>7000: ip route 172.68.0.0 s 4/3<br>
2500: ip route 171.68.0.0 s 0 </p>
<p><b>7000 Results:</b> </p>
<pre>
FRCS7-2#ping 172.68.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.68.1.1, timeout is 2 secs:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
</pre>
<p><b>2500 Results:</b> </p>
<pre>
FRCS251-1#ping 171.68.178.196
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 171.68.178.196, timeout is 2 secs:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms
</pre>
<p><b>Conclusion:</b> Like Case 3, the subnet information gets
lost since it is treated like a host route. Adding the static
routes fixes this. </p>
<hr>
</body>
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