Cisco 3750G TCAM Utilization

[sistemisti-ict]

Hello experts,
We are having strange behavior on one of our networks, it seems related to mac address table and ip arp table but we are not sure yet.

This is a stack of 3750G, they have the L3 routing and the stp root role. The stack is composed by these members:

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    2 12    WS-C3750G-12S      12.2(50)SE2           C3750-IPBASEK9-M
     3 24    WS-C3750G-24T      12.2(50)SE2           C3750-IPBASEK9-M
     4 24    WS-C3750G-24T      12.2(50)SE2           C3750-IPBASEK9-M
     5 28    WS-C3750G-24TS-1U  12.2(50)SE2           C3750-IPBASEK9-M
     6 28    WS-C3750G-24TS-1U  12.2(50)SE2           C3750-IPBASEK9-M

Investigating this problem we have issued some show commands, we have discovered non-matching values on used and max values entry on the show below.

SW-C3750# show platform tcam utilization
CAM Utilization for ASIC# 0                      Max            Used
                                             Masks/Values    Masks/values
 Unicast mac addresses:                        784/6272        152/1136
 IPv4 IGMP groups + multicast routes:          144/1152          6/26
 IPv4 unicast directly-connected routes:       784/6272        152/1136
 IPv4 unicast indirectly-connected routes:     272/2176         24/124
 IPv4 policy based routing aces:                 0/0             0/0
 IPv4 qos aces:                                768/768         260/260
 IPv4 security aces:                          1024/1024         31/31

The following shows may help you to understand the context:

SW-C3750# show mac address-table | inc Total
Total Mac Addresses for this criterion: 942

SW-C3750# show mac address-table count | inc Ava
Total Mac Address Space Available: 4408

SW-C3750# show ip arp summary
1051 IP ARP entries, with 17 of them incomplete

SW-C3750# show sdm prefer
 The current template is "desktop default" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 1024 VLANs.

  number of unicast mac addresses:                  6K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    8K
    number of directly-connected IPv4 hosts:        6K
    number of indirect IPv4 routes:                 2K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      0.5K
  number of IPv4/MAC security aces:                 1K

Can someone please clarify us if these non-matching values indicates a problem or not?
Many thanks ahead.

[gs.skills · Accepted solution]

Hello

Unicast mac addresses:                        784/6272        152/1136

you read 152/784 Masks used and 1136/6272 Values

because the TCAM is organized with up to 8 Values/Mask you can run out of Mask before you run out of Values.

the end of the output of show platform tcam utilization:

Note: Allocation of TCAM entries per feature uses
a complex algorithm. The above information is meant
to provide an abstract view of the current TCAM utilization

I don't see a problem here.

Regards, Guillaume

[sistemisti-ict]

Thanks for your explanation Guillame,

It's clear now.

[Joseph W. Doherty]

If you have access to Cisco's 3750 software, I would recommend moving from your (50)SE2 to (55)SE12.

BTW, your 12S supports templates not available on other models. When the 12S is stacked with other models, insure it uses a SDM template known to the other models.