From: Joseph Brunner (joe@affirmedsystems.com)
Date: Wed Mar 12 2008 - 20:10:40 ARST
Even though they are L3 ports, the medium is Ethernet, so layer 2
resolutions is required; CEF uses ARP to build the adjacencies, so it would
seem that once packets are moved by cef they would be layer 2 switched to
the adjacency on the other end of the cable...
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Chris Riling
Sent: Wednesday, March 12, 2008 3:56 PM
To: Cisco certification
Subject: CEF / "sh interface" Question
Hi Guys,
I have two devices connected via L3 ports (no switchport on both of them,
numbered in a /30). Here is the output of a "show interface" on one of them:
GigabitEthernet2/6 is up, line protocol is up (connected)
Hardware is C6k 1000Mb 802.3, address is 001c.0f5c.d900 (bia
001c.0f5c.d900)
Description: WLAN-3560-A
Internet address is DELETED <http://67.211.160.53/30> MTU 1500 bytes, BW
1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s
input flow-control is off, output flow-control is off
Clock mode is auto
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:02, output 00:00:02, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 2611000 bits/sec, 714 packets/sec
5 minute output rate 1819000 bits/sec, 343 packets/sec
L2 Switched: ucast: 7690293 pkt, 6192476960 bytes - mcast: 13356 pkt,
1162515 bytes
L3 in Switched: ucast: 21178092 pkt, 12095154147 bytes - mcast: 0 pkt, 0
bytes mcast
L3 out Switched: ucast: 12816194 pkt, 6605650772 bytes mcast: 0 pkt, 0
bytes
28889999 packets input, 18291572297 bytes, 0 no buffer
Received 14383 broadcasts (13356 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 11990 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
12839166 packets output, 6643457167 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out
The part I'm really interested in is this:
L2 Switched: ucast: 7690293 pkt, 6192476960 bytes - mcast: 13356 pkt,
1162515 bytes
L3 in Switched: ucast: 21178092 pkt, 12095154147 bytes - mcast: 0 pkt, 0
bytes mcast
L3 out Switched: ucast: 12816194 pkt, 6605650772 bytes mcast: 0 pkt, 0
bytes
28889999 packets input, 18291572297 bytes, 0 no buffer
Received 14383 broadcasts (13356 IP multicasts)
The mcast I can account for, because I'm running EIGRP across the link, but
why would you have such a significant amount of "L2 Switched" traffic on an
L3 interface? It seems like a dumb question, but I haven't found a good
answer yet... The obvious would be something other than IP traffic, but
that's not the case in this situation...
Thanks,
Chris
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