fast switching confusion

Answered Question
May 20th, 2007

Dear Friends,

I have learnt in one of cisco sites that

"Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis. The ip route-cache command with no additional keywords enables fast switching"

However, on one of my routers, load balancing per packet is enabled using the command "ip load-sharing per-packet"

However, on the interfact statistics, it is showing "IP fast switching is enabled". I thought fast switching will be disabled when load balancing per packet is enabled. Plz help me with this confusion. Thx in advance for ur help.

xxxxxxxxxxxxx#sh ip interface se4/3

Serial4/3 is up, line protocol is up

Internet address is xxxxxxxxxxx

Broadcast address is 255.255.255.255

Address determined by non-volatile memory

Peer address is xxxxxxxxxxxxxx

MTU is 1500 bytes

Helper address is not set

Directed broadcast forwarding is disabled

Outgoing access list is not set

Inbound access list is not set

Proxy ARP is enabled

Local Proxy ARP is disabled

Security level is default

Split horizon is enabled

ICMP redirects are always sent

ICMP unreachables are always sent

ICMP mask replies are never sent

IP fast switching is enabled

IP fast switching on the same interface is enabled

IP Flow switching is disabled

IP CEF switching is enabled

IP CEF Feature Fast switching turbo vector

IP multicast fast switching is enabled

IP multicast distributed fast switching is disabled

IP route-cache flags are Fast, CEF

Router Discovery is disabled

IP output packet accounting is disabled

IP access violation accounting is disabled

TCP/IP header compression is disabled

RTP/IP header compression is disabled

Policy routing is disabled

Network address translation is disabled

WCCP Redirect outbound is disabled

WCCP Redirect inbound is disabled

WCCP Redirect exclude is disabled

BGP Policy Mapping is disabled

I have this problem too.
0 votes
Correct Answer by mohammedmahmoud about 9 years 6 months ago

hi,

Its shown under the interface that CEF is also enabled, and CEF supports both per-packet and per-destination:

"IP CEF switching is enabled"

AFAIK this means that CEF is enabled and that any packets that fails to be CEF switched shall be fast switched.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

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Correct Answer
mohammedmahmoud Sun, 05/20/2007 - 10:26

hi,

Its shown under the interface that CEF is also enabled, and CEF supports both per-packet and per-destination:

"IP CEF switching is enabled"

AFAIK this means that CEF is enabled and that any packets that fails to be CEF switched shall be fast switched.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

Richard Burts Sun, 05/20/2007 - 17:02

Manoj

It appears that the documentation that you read is somewhat old and is from the time when the choices were fast switching and process switching. But the code that your router is running is newer and supports CEF switching. As Mohammed points out CEF supports both per destination switching and per packet switching. You are correct that the interface shows that fast switching is enabled:

IP fast switching is enabled

and Mohammed is correct that CEF switching is enabled:

IP CEF switching is enabled

and CEf switching takes precedence over fast switching.

HTH

Rick

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