Hi,
We have an office network. We'd like to intercept traffic going to
http://www.ebay.com

and slightly modify the url to:

http://rover.ebay.com/rover/1/711-1751- ... id=2316294

This will redirect them to our ebay store.

How is this possible to do?
Basically modify a url on the fly

Thanks
Phil

You need to use a proxy in order to remap URLs. I've never done this in MikroTik, but the documentation should tell you how.

Use 'transparent proxy' that allows to avoid proxy browser configuration for end user,
add rule to access list that will contain,
'ip proxy access dst-host=...ebay... redirect-to=...rover.ebay...'.

So my router for the office can also be a proxy server? and not use up the resources of the router?

Yes, MikroTik RouterOS can provide you with proxy support.
Note, that proxy does not make that proxy is not using upstream resources at all.
Proxy can cache either HTTP (static pages and images), FTP protocol, other traffic is not cached by the proxy.

Tried to use

'ip proxy access dst-host=...ebay... redirect-to=...rover.ebay...'.

Error no command redirect-to

In this post you can find it http://forum.mikrotik.com/viewtopic.php?f=2&t=17411

But here you are:
You must have instaled webproxy-test package!!!

Regards,
Mladen

Ok I tried this
[admin@disd] ip proxy access> add action=deny dst-host="www.myspace.com" redirect-to="www.dictionary.com"

and get this error

no such argument (redirect-to)

This error is shown, because 'web-proxy test' package is not installed.
Make sure 'system package print' gives you,

system package print
6 webproxy-test

and not,
system package print
6 X webproxy-test

0 routeros-x86 2.9.44
1 system 2.9.44
2 X rstp-bridge-test 2.9.44
3 web-proxy 2.9.44
4 ups 2.9.44
5 synchronous 2.9.44
6 X webproxy-test 2.9.44
7 routerboard 2.9.44
8 ntp 2.9.44
9 wireless 2.9.44
10 X wireless-legacy 2.9.44
11 hotspot 2.9.44
12 dhcp 2.9.44
13 X routing-test 2.9.44
14 routing 2.9.44
15 ppp 2.9.44
16 security 2.9.44
17 advanced-tools 2.9.44

So how do you get Web Proxy Test?

'X' means it is disabled.

select it and then click enable and then restart system.

system package enable webproxy-test
system reboot