WCCP: Cat6k & Mask Assignment

[abeywick]

Hi,

We are developing wccp V2 software to redirect tcp/udp packets from Cisco routers.

We are having a problem with Cat6k when capability mask assignment is requested in Here-I-Am (methods selected from offered capabilities: L2 fwd, mask assignment, gre return). Cat6k shows that client is still in "Not Usable" state.

Please see Cat6k output:

Router#show ip wccp 97 detail

WCCP Cache-Engine information:

Web Cache ID: 3.3.3.2

Protocol Version: 2.0

State: NOT Usable

Redirection: L2

Packet Return: GRE

Packets Redirected: 0

Connect Time: 00:35:19

Assignment: MASK

Debug msg on cat6k shows:

WCCP-EVNT:wccp_validate_wc_assignments: no mask data, exit

WCCP-EVT:D97: Here_I_Am packet from 3.3.3.2 with incompatible assignment data

1. Are we supposed to send more info (mask info?) in the Here-I-AM msg that is not specified in the WCCP v2 draft?

2. Is the Cat6k expecting a Redirect Assignment msg from the Designated Web Cache to make a web-cache usable when mask assignment is used? (from our interpretation of the draft, Designated web-cache should not use any web-cache that is not listed in router I-See-U. When we sent a Redirect Assign msg to experiment, while the web-cache was in “Not Usable” state, Cat6k shows this message:

" WCCP-EVNT:D97: Redirect_Assignment packet from 3.3.3.2 fails source check.

3. Is there a developer's guide/spec/packet format available other than the WCCP v2 draft?

We have successfully redirected tcp/udp packets with L2-rewrite Cat6k using hash assignment method. We are running IOS 12.2.

Thanks in advance.

[Gilles Dufour · Accepted solution]

In the Web-cache Identity Info component the flag indicating mask assignment should be set. Also there should be a single mask-value set defined containing the mask configured on the cache.

You should maybe buy a small Cisco cache engine and sniff the communication between the cache and router 🙂

There is no external info that I know about regarding wccp packet format.

Gilles.

[abeywick]

Gilles,

That was an excellent piece of information. We had no idea that reserved fields and hash bucket info were used for mask assignments. It looks like mask assignment feature is a Cisco propriety extension. Without your hint we would have been in total darkness!

If it is possible for other companies to purchase this specification, please let us know (btw, we are not building another web-cache, just want to use WCCP to redirect traffic).

We reverse engineered the ICU packets and got TCP packets redirected using the mask assignment. We have a couple of more questions:

1. Is it possible to redirect UDP packets also?

(was able to do so with hash assign.)

2. Is there a mask value that can tell the

router to redirect all packets?

Thanks in advance.

Harsha

[pgolding]

Harsha,

Have a look at the IOS command "show ip wccp service", from where you may be able to determine how the wccp packet fields map to the service. I believe that a protocol must be configured (i.e. 0 is not an option), so redirecting all packets cant be done with the one service. UDP is fair game though, services like 81, 82, 83 use it now.

I cant say what difference mask assign might make but mask does support the same services as hash, so the above should also apply.

There is no single document that fully details WCCP, so the specification is not available.

Regards, Peter

[abeywick]

Peter, Gilles,

Thanks a lot for your responses. We successfully implemented L2 redirect with mask assignment.

We noticed that web-cache id element is missing 8 bytes of bucket block in the ICU pkt when the flag is set to 0x2 and it's of regular size when it's 0x3. We are interpreting this 0x1 bit as "this web-cache is not selected for redirect".

UDP redirect works when we use redirect out on the egress vlan. We will investigate why redirect in does not work.

We may run into issues in the future if Cisco changes the message formats as wccp v2 draft is the only doc we have.

thanks again.

Harsha