[c-nsp] Whats happens when TCAM is full on 7600/RSP720RSP-3CXL?

[chiel]

Hi,

I'm currently using a 7606 (RSP720RSP-3CXL) and taking in full BGP on v4 
and v6. Obviously it the TCAM is almost full and the box needs to be 
replaced.

But a have a couple of questions.

I have been hearing different scenario of what would happen when the 
TCAM is full:
1. The whole thing goes into software routing mode for all routes which 
causes 100% CPU and resulting and unusable box
2. New route entries will just get dropped, current entries just stay in 
TCAM
3. New route entries will be software routed, but entries that are 
already in TCAM will be hardware routed. You won't notice much impact in 
the beginning.

What is true?

The only reason that our 7606 needs to be replaces it because of the 
TCAM. It doesn't do much traffic, like 3Gbps upstream. Only BGP/OSPF. 
And not many ports, 8 x 10Gb fiber + 30 x 1Gb copper (local servers).

We will probably go for the ASR9006. But I would like to use it like I'm 
using the 7600 now, as a router/switch. I have been reading that you 
need to make some uncommon config to create Ethernet VLAN/Trunk 
interfaces and ports, as this is not commonly not done with this router. 
But is this good practice? Will it be fine once I fingered it out?

Last question. Can I take a full BGP feed on both v4 and v6 with a 
A9K-RSP440-TR? Or do I need the -SE?

Chiel



Bellow are some output of our current 7600:

#show mls cef maximum-route
  IPv4 + MPLS         - 832k (default)
  IPv6                - 90k
  IP Multicast        - 1k

#show mls cef su
Total routes:                     915422
     IPv4 unicast routes:          822144
     IPv4 Multicast routes:        8
     MPLS routes:                  2050
     IPv6 unicast routes:          91220
     IPv6 multicast routes:        3
     EoM routes:                   0

#show mls cef exception status
Current IPv4 FIB exception state = FALSE
Current IPv6 FIB exception state = FALSE
Current MPLS FIB exception state = FALSE

#show platform hardware capacity forwarding
L3 Forwarding Resources
  Module              FIB TCAM usage: Total        Used     %Used
    2                     72 bits (IPv4, MPLS, EoM)      851968 
824115     97%
                         144 bits (IP mcast, IPv6)       98304 91198     93%