IP Routing
6-12
8000-A2-GB21-30
April 1998
With Source-Based Routing
With source-based routing, the source address of upstream packets sent from an
ES are compared to the source address listed in the static route table. If a match
is found, the packet is sent to the next-hop address specified for that source
address.
The following illustration shows the packet flow when ES1 sends to ES2, and
when source-based routes are defined for ES1 and ES2 (indicated by the S/D
flag).
97-15473-0
Router
155.1.3.1
DSL Card*
s1c
RTU 1*
135.1.3.3
155.1.3.4
ES1
s1d
RTU 2*
135.1.3.4
155.1.3.5
ES2
Packet Flow
e1a
155.1.2.1
NSP
155.1.2.2
Host/Net
1) 155.1.3.4
2) 155.1.3.5
Subnet Mask
255.255.255.255
255.255.255.255
Next-Hop Address
155.1.3.1
155.1.3.1
S/D (Source/Destination)
src (source)
src (source)
Partial DSL Routing Table
*If DSL card is an 8540 DSL card,
associated RTU will not have an IP address.
Upstream packets from ES1 (and ES2) are sent to 155.1.3.1, where in turn the
router would forward them to the NSP. Downstream packets from the NSP are
sent to ES2.
For upstream packets only (i.e., packets arriving over the DSL ports), the order of
routing precedence is:
1. Source host route
2. Source subnet route
3. Source network route
4. Destination host route
5. Destination subnet route
6. Destination network route
7. Default route
NOTE:
When using source routing, do not use the default route.
