CEF and Trunks

[rugman66]

Hello,

Below is the general question, I can provide any sh command output.

I have a router with several VLAN’s configured, and need to have a trunk from the router to

a c4948 switch. With global and interface CEF enabled on the router layer 2 trunk GigE interface it is not

using CEF but is process switching packets, and that is bringing throughput to a crawl. If I change

the router and switch interfaces to layer 3 and assign IP’s to both will the link be able to forward

packets from all VLAN’s due to the FIB? How can I enable CEF on this link?

  Thank you

[Georg Pauwen]

Hello,

CEF is a layer 3 switching technology and has nothing to do with trunks. What are you trying to configure, a router on a stick ?

[rugman66]

I have a router running several vlan's with a trunking GigE interface that connects to a c4948 trunking GigE interface. The inbound queue of the router interface is dropping packets at a massive rate because it is process switching due to not CEF processing. What would be the best configuration to increase throughput?

Both trunk ports have the following configuration

Router

Name: Gi1/0

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: Disabled

Access Mode VLAN: 0 ((Inactive))

Trunking Native Mode VLAN: 1 (default)

Trunking VLANs Enabled: ALL

Trunking VLANs Active: 1-2,5-8,10

Protected: false

Priority for untagged frames: 0

Override vlan tag priority: FALSE

Voice VLAN: none

Appliance trust: none

Switch

Name: Gi1/48

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: Off

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk private VLANs: none

Operational private-vlan: none

Trunking VLANs Enabled: 1,2,5-8,10

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Thank you

[Georg Pauwen]

Hello,

post the output of 'show interfaces x' for both interfaces...

[rugman66]

Sure,

Router port

#sh interfaces gigabitEthernet 1/0
GigabitEthernet1/0 is up, line protocol is up
  Hardware is Gigabit Ethernet, address is c471.fe4a.9b4b (bia c471.fe4a.9b4b)
  Description: Trunk to 4948_left
  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 set (10 sec)
  output flow-control is off, input flow-control is off
  0 pause input, 0 pause output
  Full-duplex, 1000Mb/s
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:01, output never, output hang never
  Last clearing of "show interface" counters 2w6d
  Input queue: 0/100/42251936/0 (size/max/drops/flushes); Total output drops: 13597
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 189000 bits/sec, 106 packets/sec
  5 minute output rate 523000 bits/sec, 108 packets/sec
     1145572748 packets input, 1645937597 bytes, 0 no buffer
     Received 883100 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     4071 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     1870048228 packets output, 1250264857 bytes, 0 underruns
     1 output errors, 0 collisions, 0 interface resets
     2767 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

Switch port

#sh interfaces gigabitEthernet 1/48
GigabitEthernet1/48 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet Port, address is 001d.a26e.c42f (bia 001d.a26e.c42f)
  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, link type is auto, media type is 10/100/1000-TX
  Media-type configured as RJ45 connector
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:01, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 462000 bits/sec, 105 packets/sec
  5 minute output rate 184000 bits/sec, 110 packets/sec
     17731231901 packets input, 20773959580119 bytes, 0 no buffer
     Received 65887959 broadcasts (56821798 multicast)
     0 runts, 0 giants, 0 throttles
     1 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored
     0 input packets with dribble condition detected
     13275562125 packets output, 6161807353824 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

Thank you

[Georg Pauwen]

Hello,

on your router, change the hold queue to 2000 (which equals the hold queue on the other side):

Router#conf t

Router(config)#int gigabitEthernet 1/0

Router(config-if)#hold-queue 2000 in

Router(config-if)#end

[rugman66]

I increased the router interface inbound queue to 2000 and no change in inbound queue packet drops.

Thank you

-John

[Georg Pauwen]

Hello,

what is the output of 'show interfaces GigabitEthernet0/1 switching' (this is a hidden command so you need to type the entire string) ?

Have you enabled fast switching on the router and/or the interface ?

interface GigabitEthernet0/1

ip route-cache

What platform is this anyway (e.g. 3925, 4331) ?

[rugman66]

Hi,

This is a 3845 router, and the interface is a layer 2 trunk, can't enable ip route-cache

Sorry about the formatting of the show command below.

#sh interfaces gigabitEthernet 1/0 switching
GigabitEthernet1/0 Trunk
          Throttle count          0
                   Drops         RP   49493936         SP          0
             SPD Flushes       Fast          0        SSE          0
             SPD Aggress       Fast          0
            SPD Priority     Inputs          0      Drops          0

    Protocol  DEC MOP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process          0          0       3420     263340
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  Spanning Tree
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process        509      22224    8212372  521485580
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  CDP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process      34128   14353782      34252   13255524
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  VTP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process          0          0       3492     360084
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

    Protocol  Other
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process       2812     168720          0          0
            Cache misses          0          -          -          -
                    Fast          0          0          0          0
               Auton/SSE          0          0          0          0

[rugman66]

The VLAN’s are configured with default route on the router, but not as subinterfaces on the GigE

trunk interface. If I perform the following steps I should avoid process switching and be able to use CEF on the GigE interface correct?

1. Remove the existing VLANS with default IP’s
2. Create 802.1q VLAN subinterfaces with default IP’s on the layer 3 GigE interface connected to the switch
3. Enable CEF on each subinterface

Then CEF and not process switching should be used correct?

Thank you

[Georg Pauwen]

Hello,

your traffic volume is low, there should be no drops at all. Are these RJ-45, GBIC, or SFP connections ? Try to set the media type on the interface of the 3845, also increase the output hold queue and the queuing strategy:

interface GigabitEthernet1/0

fair-queue

hold-queue 2000 out

media-type gbic/rj45/sfp

[paul driver]

Hello

---

@rugman66 wrote:

Hello,

 How can I enable CEF on this link?

---

On the physical or SVI interface:

int x/x
ip route-cache cef
end
show ip int x/x | in IP