[c-nsp] Missing 'packet-too-big' ICMPs on 12.2(28)SB6
Gerald Krause
gk at ax.tc
Tue Sep 11 09:53:54 EDT 2007
Karol Mares wrote:
> Hi,
>
> On 9/10/07, Gerald Krause <gk at ax.tc> wrote:
>> Gerald Krause wrote:
>>> Hi,
>>>
>>> I have a 7206VXR as LNS under 12.2(28)SB6 and wonder if anyone
>>> experience a strange ICMP behaviour regarding fragmentation/MTU
>>> bounderies. It seems that the router doesn't generate appropriate
>>> ICMP messages when pakets arrive that the system can't (or isn't
>>> allow to) fragment.
>>>
>>> The only problem with our config could be the fact that we have
>>> configured a MTU of 1530 byte (because of MPLS) on the FEs. But even
>>> if this could be problematic I would expect that in the case that a
>>> paket arrive which can't be delivered through the VirtualInterfaces
>>> (MTU 1448 byte) the system have to mention that in the logging buffer.
>>> Thats why I have enabled ICMP debugging and related CEF debugging
>>> but I never see 'packet-too-big' ICMP messages, only 'echo' and
>>> 'host/port unreachable' messages are logged. But I See that CEF is
>>> aware of the fact that it can't deliver the packet without
>>> fragmentation:
>>>
>>>
>>> debug:
>>> ======
>>> Generic IP:
>>> ICMP packet debugging is on
>>> IP CEF:
>>> IP CEF drops debugging is on
>>> for access list 80
>>> IP CEF fragmentation debugging is on
>>>
>
>
> Curious, can you show me the show int fa<x> and show ip traffic command ?
Yep, sure:
#sh int fa0/0
FastEthernet0/0 is up, line protocol is up
Hardware is DEC21140A, address is 0050.0b3b.5400 (bia 0050.0b3b.5400)
Description:
Internet address is x.x.x.x/27
MTU 1530 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 9/255, rxload 21/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 1/75/133/4658 (size/max/drops/flushes); Total output
drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 8480000 bits/sec, 2907 packets/sec
5 minute output rate 3777000 bits/sec, 1939 packets/sec
2643939396 packets input, 3280004591 bytes, 5 no buffer
Received 16131045 broadcasts (0 IP multicast)
0 runts, 0 giants, 138 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog
0 input packets with dribble condition detected
3432839522 packets output, 1002457105 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 babbles, 0 late collision, 0 deferred
1 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
#sh int fa4/0
FastEthernet4/0 is up, line protocol is up
Hardware is DEC21140, address is 0050.0b3b.5470 (bia 0050.0b3b.5470)
Description:
Internet address is y.y.y.y/27
MTU 1530 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 13/255, rxload 3/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/3006 (size/max/drops/flushes); Total output
drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 1500000 bits/sec, 368 packets/sec
5 minute output rate 5187000 bits/sec, 1432 packets/sec
2845013786 packets input, 2383827726 bytes, 0 no buffer
Received 15908291 broadcasts (0 IP multicast)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog
0 input packets with dribble condition detected
1842783025 packets output, 2416455042 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 babbles, 0 late collision, 0 deferred
1 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
#sh ip traffic
IP statistics:
Rcvd: 250484026 total, 159198119 local destination
1576 format errors, 0 checksum errors, 884039 bad hop count
4 unknown protocol, 35458 not a gateway
0 security failures, 0 bad options, 36188 with options
Opts: 8 end, 0 nop, 0 basic security, 0 loose source route
0 timestamp, 0 extended security, 8 record route
0 stream ID, 0 strict source route, 36180 alert, 0 cipso, 0 ump
0 other
Frags: 44235703 reassembled, 42 timeouts, 0 couldn't reassemble
41228174 fragmented, 1072 couldn't fragment
Bcast: 8313647 received, 0 sent
Mcast: 29135477 received, 9634176 sent
Sent: 206325022 generated, 2459945607 forwarded
Drop: 1677 encapsulation failed, 0 unresolved, 0 no adjacency
216 no route, 0 unicast RPF, 0 forced drop
0 options denied, 4 source IP address zero
ICMP statistics:
Rcvd: 13 format errors, 220 checksum errors, 93697 redirects,
33291 unreachable
1769784 echo, 6415 echo reply, 0 mask requests, 0 mask
replies, 29 quench
0 parameter, 0 timestamp, 0 info request, 0 other
0 irdp solicitations, 0 irdp advertisements
Sent: 0 redirects, 2399844 unreachable, 6609 echo, 1769783 echo reply
0 mask requests, 0 mask replies, 0 quench, 0 timestamp
0 info reply, 819068 time exceeded, 0 parameter problem
0 irdp solicitations, 0 irdp advertisements
UDP statistics:
Rcvd: 66735466 total, 9 checksum errors, 3325761 no port
Sent: 177825189 total, 0 forwarded broadcasts
TCP statistics:
Rcvd: 25385141 total, 2532 checksum errors, 4059 no port
Sent: 18698403 total
Probe statistics:
Rcvd: 0 address requests, 0 address replies
0 proxy name requests, 0 where-is requests, 0 other
Sent: 0 address requests, 0 address replies (0 proxy)
0 proxy name replies, 0 where-is replies
BGP statistics:
Rcvd: 20697361 total, 11 opens, 0 notifications, 20281798 updates
415544 keepalives, 8 route-refresh, 0 unrecognized
Sent: 801874 total, 11 opens, 2 notifications, 15207 updates
786648 keepalives, 6 route-refresh
OSPF statistics:
Rcvd: 20774889 total, 0 checksum errors
13832619 hello, 1109278 database desc, 5 link state req
3295510 link state updates, 2537453 link state acks
Sent: 4781925 total
2307649 hello, 46631 database desc, 8 link state req
1777298 link state updates, 650641 link state acks
IP-EIGRP statistics:
Rcvd: 0 total
Sent: 0 total
PIMv2 statistics: Sent/Received
Total: 0/0, 0 checksum errors, 0 format errors
Registers: 0/0 (0 non-rp, 0 non-sm-group), Register Stops: 0/0,
Hellos: 0/0
Join/Prunes: 0/0, Asserts: 0/0, grafts: 0/0
Bootstraps: 0/0, Candidate_RP_Advertisements: 0/0
Queue drops: 0
State-Refresh: 0/0
IGMP statistics: Sent/Received
Total: 4/0, Format errors: 0/0, Checksum errors: 0/0
Host Queries: 0/0, Host Reports: 0/0, Host Leaves: 0/0
DVMRP: 0/0, PIM: 0/0
Queue drops: 0
ARP statistics:
Rcvd: 2651898 requests, 13186 replies, 0 reverse, 0 other
Sent: 14493 requests, 39548 replies (0 proxy), 0 reverse
Drop due to input queue full: 0
--
Gerald (ax/tc)
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