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4451-X and 4351 SVI interfaces act diffrently in regard to MTU size supported

westj
Level 1
Level 1

I have two routers, a ISR4451-X and a ISR43 connected to several layer three switches (3750X). I am using 8 port NIM-ES2-8 modules to connect the routers to the switches with SVIs. The problem is that from the 4351 to device behind the switches it can only ping with packets <500 bytes. but the 4451-X can ping targets downstream from the 3750s with a 2000 byte packet.

Here is the IOS they are running:

System image file is "bootflash:isr4400-universalk9.03.16.01a.S.155-3.S1a-ext.SPA.bin"
System image file is "bootflash:isr4300-universalk9.03.16.01a.S.155-3.S1a-ext.SPA.bin"

Here is a ping from both routers (10.220.18.20 is across the interfaces shown below)

4451-A#ping 10.220.18.20 size 2000
Type escape sequence to abort.
Sending 5, 2000-byte ICMP Echos to 10.220.18.20, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
4351-B#ping 10.220.18.20 size 2000
Type escape sequence to abort.
Sending 5, 2000-byte ICMP Echos to 10.220.18.20, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
4351-B#ping 10.220.18.20 size 450
Type escape sequence to abort.
Sending 5, 450-byte ICMP Echos to 10.220.18.20, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
4351-B#ping 10.220.18.20 size 500
Type escape sequence to abort.
Sending 5, 500-byte ICMP Echos to 10.220.18.20, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

Here are the relevant router configs:

4451-A#sr g0/1/4
Building configuration...

Current configuration : 138 bytes
!
interface GigabitEthernet0/1/4
 description to
 switchport access vlan 352
 switchport mode access
 spanning-tree portfast
end
!
interface Vlan352
 ip address 192.168.23.54 255.255.255.252
4351-B#sr g0/1/7
Building configuration...

Current configuration : 158 bytes
!
interface GigabitEthernet0/1/7
 description to
 switchport access vlan 360
 switchport mode access
 spanning-tree portfast
end
!
interface Vlan360
 ip address 192.168.23.62 255.255.255.252

Does anyone know how I can get the 4351 to pass larger packets? I tried MTU 2000, but that didn't seem to work. I am looking at SM-X-ES3-24-P to get a true layer 3 switch in the routers and get away from the SVIs, but I would like to get this working while I wait for the new switch.

Any suggestions?

Thanks

5 Replies 5

Philip D'Ath
VIP Alumni
VIP Alumni

Could you post the outptut of the "show interface ..." for the two physical interfaces.  I'm really only interested in the MTU part.  Ditto for the two SVI interfaces.

See above.

Thanks.

The outputs all have an MTU of 1500 bytes - so I don't think this issue is the routers.

I think the issue is what they are plugging into, or downstream of that.

If you do a "show ip route 10.220.18.20 ..." is it definitely going via the two SVI's listed above?  It isn't going out some other path is it?

Can you show the "show interface" output of the two switch ports (on the 3750-Xs) that they are plugging into, plus the two related SVIs?  I only need to see the MTU line.

For some reason the clipboard is not working in SecureCRT on my TeamViewer session so I can't paste the IP route info right now, but I just checked both routers and they are going down the ports in question.

All ports on the 3750X are "MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255". The 3750s are stacked, for what it is worth.

That is why I am stumped, the only difference is the 4451-X vs. 4351.

westj
Level 1
Level 1

Here is the output, the ports on the 4351 are shut but the output is the same when they are up.

4451-A#sh int g0/1/4
GigabitEthernet0/1/4 is up, line protocol is up (connected)
  Hardware is NIM-ES2-8, address is 5c83.8f84.f4fc (bia 5c83.8f84.f4fc)
  Description:
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive not supported
  Full-duplex, 1000Mb/s, media type is RJ45
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:59, output 00:00:07, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 662000 bits/sec, 524 packets/sec
  5 minute output rate 1727000 bits/sec, 163 packets/sec
     16091461 packets input, 2608761351 bytes, 0 no buffer
     Received 126 broadcasts (6886 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 6886 multicast, 0 pause input
     0 input packets with dribble condition detected
     1662167 packets output, 1984494507 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 unknown protocol drops
     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
4451-A#sh int vl 352
Vlan352 is up, line protocol is up
  Hardware is Ethernet SVI, address is 5c83.8f84.f574 (bia 5c83.8f84.f574)
  Internet address is 192.168.23.54/30
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive not supported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 01:26:46, output 01:26:46, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 654000 bits/sec, 519 packets/sec
  5 minute output rate 1733000 bits/sec, 163 packets/sec
     16083419 packets input, 2543501576 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     1661062 packets output, 1983725311 bytes, 0 underruns
     0 output errors, 1 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
4351-B#sh int g0/1/7
GigabitEthernet0/1/7 is administratively down, line protocol is down (disabled)
  Hardware is NIM-ES2-8, address is e865.496c.24df (bia e865.496c.24df)
  Description:
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive not supported
  Auto-duplex, Auto-speed, media type is RJ45
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 08:18:35, output 08:18:31, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 7000 bits/sec, 8 packets/sec
  5 minute output rate 8000 bits/sec, 7 packets/sec
     20273 packets input, 2281348 bytes, 0 no buffer
     Received 6 broadcasts (490 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 490 multicast, 0 pause input
     0 input packets with dribble condition detected
     14743 packets output, 3441644 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 unknown protocol drops
     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
4351-B#sh int vl 360
Vlan360 is down, line protocol is down
  Hardware is Ethernet SVI, address is e865.496c.2554 (bia e865.496c.2554)
  Description: to E-UTRAN stack
  Internet address is 192.168.23.62/30
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive not supported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 08:20:47, output 08:20:47, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     19951 packets input, 2152796 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     14548 packets output, 3406805 bytes, 0 underruns
     0 output errors, 1 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out

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