Sidewinder G2 6.1.2 Administration Guide - Glossary of Technical ...

Appendix D: Configuring Dynamic Routing with RIP
RIP with Sidewinder G2 using transparent IP addressing
If connection is lost
between Router_a
and SidewinderG2_b
618
hops verses 4 hops), it forwards the connection frame on to Router_a, which
forwards the frame to the Sidewinder G2. The Sidewinder G2 IP services
receive the frame, and checks its routing table to decide if it knows where this
connection request should be sent.
Because the external routing table has a route to Bizco’s network, the IP
services sends the request up to the Telnet proxy. If there was no route to
Bizco’s network, and a default route had not been specified, the Sidewinder G2
IP services would have discarded the packet. The Telnet proxy receives and
validates the connection request, then proceeds to issue a new, independent
TCP connection request to the Telnet server (on the external network). This
new request, which has an originating address of the external Sidewinder G2,
gets sent to Router_a and is forwarded on into the Bizco network and so on
and so forth. The Bizco Telnet server replies back to the Sidewinder G2,
thinking that the Sidewinder G2 is the originator of the session. The Telnet
proxy then replies back to the Telnet client, and the session is now in place
between the server and the client.
If the connection between Router_a and SidewinderG2_b is lost, the following
occurs:
1 SidewinderG2_b notices that it is no-longer receiving RIP updates from
Router_a and updates its local routing table hop count for that route to 16
(route unreachable), and broadcasts this out on the internal network (this is
to notify Router_b).
2 The Telnet client sends another IP frame to Router_a unaware that the
route between Router_a-to-SidewinderG2_b has been lost. Router_a looks
at its local routing table and discovers there are two routes, one
unreachable, the other through Router_d.
3 Because Router_d is on the same network as the client, Router_b sends an
‘ICMP Redirect’ back at the client stating that it can reach the Telnet server
network through Router_d.
4 The client updates its local routing table to point that host at Router_d, then
re-sends its last frame to Router_d.
5 Router_d receives the frame and forwards it on to Router_c, which
forwards it on to SidewinderG2_c.
6 SidewinderG2_c, receives the IP frame for the Telnet server, checks the
route, has a route, and sends it up to the internal TCP servers. The
Sidewinder G2 TCP services checks the frame and discovers this is not a
TCP connection request and that it there is not currently a session with the
client. Because of this, TCP services builds a ‘TCP reset’ frame and sends
it back to the client.
Note: This causes the current Telnet session to be lost. However, when the Telnet
client opens another session to the server, that connection request will get sent to
SidewinderG2_c, which will go through all the above steps and establish a NEW
session with the Telnet server.