Packet Walk-Throughs
9-6
8000-A2-GB21-30
April 1998
97-15479-0
Router
135.1.1.2
135.1.2.1
135.1.3.254
DCE
Manager
WS1
135.1.1.1
MCC Card
e1a:135.1.2.2
RTU
135.1.3.4
8546 DSL
Card
s1b:135.1.3.2
Unnumbered
Interface
s1b:135.1.3.1
1) 135.1.3.4
2) 0.0.0.0
135.1.3.2
135.1.2.1
Host/Net Subnet Mask
255.255.255.255
0.0.0.0
Next-Hop Address S/D (Source/Destination)
dst (destination)
dst (destination)
MCC Routing Table
1) 135.1.2.0
2) 135.1.1.0
3) 135.1.3.4
135.1.3.1
135.1.3.1
135.1.3.4
Host/Net Subnet Mask
255.255.255.0
255.255.255.0
255.255.255.0
Next-Hop Address S/D (Source/Destination)
dst (destination)
dst (destination)
dst (destination)
Partial DSL Routing Table
RTU issues reply to ping
WS1 pings the RTU
12345
1 2 3 4 5 6 7 8
When WS1 pings a Hotwire RTU:
1. The packet addressed to 135.1.3.4 is routed to the router by normal means.
2. The router then does an ARP request for the RTU because the router’s IP
address of 135.1.3.254 is on the same subnetwork as the RTU (with an IP
address of 135.1.3.4).
Note that the router’s interface to the MCC is multihomed (i.e., it has two IP
addresses (135.1.2.1 and 135.1.3.254) assigned to the one interface).
3. The MCC does an ARP reply with its own MAC address (proxy ARP).
4. The router then forwards the ping packet to the MCC card.
5. Upon receiving the ping, the MCC card consults its routing table to identify to
which 8546 DSL card to forward the ping.
In this case, route #1 contains a host route for 135.1.3.4 with a next hop of
DSL 135.1.3.2.
6. The ping request is then forwarded to the 8546 DSL card from the MCC
card’s
s1b
interface to the 8546 DSL card’s
s1b
interface (which is over the
DSLAM system backplane).
7. From the routing table, the 8546 DSL card determines that 135.1.3.4 is
directly connected over s1c (one of the 8546 DSL card’s DSL ports).
8. The 8546 DSL card then forwards the ping to the RTU over s1c.
