09.12.2012 Views

Understanding the network.pdf - Back to Home

Understanding the network.pdf - Back to Home

Understanding the network.pdf - Back to Home

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

outer#show ip masks 172.16.0.0<br />

Mask Reference count<br />

255.255.255.255 4<br />

255.255.255.252 1<br />

255.255.255.248 2<br />

255.255.255.128 1<br />

255.255.255.0 6<br />

255.255.248.0 3<br />

A problem commonly associated with dynamically addressed <strong>network</strong>s is incorrect<br />

ARP table entries. For example, a node's IP address can change or a new IP address<br />

is assigned <strong>to</strong> a node that already had an address on <strong>the</strong> same segment (an expired<br />

DHCP lease, perhaps). These are prime targets for bad ARP entries. Since <strong>the</strong> router<br />

plays such an important role in data delivery for all <strong>the</strong> connected nodes, it is<br />

essential that <strong>the</strong> router's ARP table be correct. A good place <strong>to</strong> start looking when<br />

nodes are suddenly unreachable and no hardware failure exists is <strong>the</strong> router's ARP<br />

tables. Like <strong>the</strong> IP routing table, <strong>the</strong> ARP table is viewable in user EXEC mode. To<br />

display <strong>the</strong> ARP table, <strong>the</strong> command is used:<br />

Router>show arp<br />

Internet 192.168.191.220 - 00e0.1ef2.15a1 ARPA E<strong>the</strong>rnet2/0<br />

Internet 192.168.191.253 0 00c0.4906.9488 ARPA E<strong>the</strong>rnet2/0<br />

Internet 192.168.191.240 0 00e0.1e34.a758 ARPA E<strong>the</strong>rnet2/0<br />

Internet 192.168.191.141 37 00e0.b08d.ccf0 ARPA E<strong>the</strong>rnet2/0<br />

Internet 192.168.191.142 41 00e0.1e5b.6e80 ARPA E<strong>the</strong>rnet2/0<br />

Internet 192.168.190.136 - 00e0.1ef2.15b1 ARPA E<strong>the</strong>rnet3/0<br />

Internet 192.168.190.137 - 00e0.1ef2.15b1 ARPA E<strong>the</strong>rnet3/0<br />

Internet 192.168.190.138 - 00e0.1ef2.15b1 ARPA E<strong>the</strong>rnet3/0<br />

Internet 192.168.190.139 - 00e0.1ef2.15b1 ARPA E<strong>the</strong>rnet3/0<br />

A great <strong>to</strong>ol for displaying information about <strong>the</strong> dynamic IP routing pro<strong>to</strong>cols<br />

running on <strong>the</strong> router is . This command can display a verbose<br />

or terse report. Verbose is <strong>the</strong> default, and it displays all <strong>the</strong> running processes,<br />

<strong>the</strong>ir update status, <strong>the</strong> <strong>network</strong>s being announced, and any neighbor routers:<br />

ASBR-34#sh ip pro<strong>to</strong>cols<br />

Routing Pro<strong>to</strong>col is "bgp 66"<br />

Sending updates every 60 seconds, next due in 0 seconds<br />

Outgoing update filter list for all interfaces is

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!