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Direction | Source Addr. | Dest. Addr. | Protocol | Source Port | Dest. Port | ACK Set | Notes |
---|---|---|---|---|---|---|---|
In | Ext | Int | UDP | >1023 |
3130[44]
|
[45]
|
ICP request or response, external cache to internal cache |
Out | Int | Ext | UDP | 3130[44] | >1023 | [45] | ICP request or response, internal cache to external cache |
In | Ext | Int | TCP | >1023 |
3128[46]
|
[47]
|
HTTP request, external cache to internal cache |
Out | Int | Ext | TCP | 3128[46] | >1023 | Yes | HTTP response, internal cache to external cache |
Out | Int | Ext | TCP | >1023 | 3128[46] | [47] | HTTP request, internal cache to external cache |
In | Ext | Int | TCP | 3128[46] | >1023 | Yes | HTTP response, external cache to internal cache |
[44]3130 is the standard port number for ICP, but some servers run on different port numbers.
[45]UDP has no ACK equivalent.
[46]3128 is the standard port number for intercache HTTP servers, but some servers run on different port numbers.
[47]ACK is not set on the first packet of this type (establishing connection) but will be set on the rest.
Since ICP is a straightforward TCP-based protocol, it would also be possible to proxy it through a proxy system like SOCKS; the only difficulty is that you would end up with a one-way relationship, since the external cache would not be able to send queries to the internal cache. This would slow down performance without providing any more security than doing self-proxying, and no current implementations support it.
Direction | Source Addr. | Dest. Addr. | Protocol | Source Port | Dest. Port | Notes |
---|---|---|---|---|---|---|
In | Ext | Int | UDP |
[48]
|
2048 | WCCP update, external participant to internal participant |
Out | Int | Ext | UDP | [48] | 2048 | WCCP update, internal participant to external participant |
In | Ext | Int | GRE |
[49]
|
[49] | HTTP query redirected by external router to internal cache server |
Out | Int | Ext | GRE | [49] | [49] | HTTP query redirected by internal router to external cache server |
[48]The WCCP protocol does not define a source port; it is likely to be 2048.
[49]GRE does not have source or destination ports, only protocol types. WCCP uses protocol type hexadecimal 883E.