IP Routing
6-10
8000-A2-GB21-20
November 1997
Source-Based Routing
In addition to destination-based routing, the HotWire DSLAM system also
supports source-based routing. Source-based routing is a security feature for
preventing ES-to-ES routing when they are attached to different RTUs that are
attached to the same DSL card. That is, sourced-based routing can ensure that
all upstream traffic within a service domain is sent to the NSP.
Without Source-Based Routing
The following illustration shows that with destination routing ES1 can send
packets to ES2 based on the static route table. That is, when ES1 sends a packet
to ES2, the destination route is 155.1.3.5 and the next hop address for this
destination is 135.1.3.4 (RTU 2).
97-15472-02
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
Host/Net
1) 155.1.3.4
2) 155.1.3.5
3) 0.0.0.0
Subnet Mask
255.255.255.255
255.255.255.255
0.0.0.0
8546 DSL
Card Next-Hop
Address
135.1.3.3
135.1.3.4
155.1.3.1
S/D (Source/
Destination)
dst (destination)
dst (destination)
dst (destination)
DSL Routing Table
*If DSL card is an 8540 DSL card,
associated RTU will not have an IP address.
s1c
s1d
155.1.3.1
8540 DSL
Card Next-Hop
Address
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).
