Paradyne 8540 Network Configuration Manual page 69

IP Filtering
7-6
In the following illustration, ES2 spoofs ES1's IP address (that is, ES2 assumes
ES1's IP address of 155.1.3.4):
NSP1 Router
155.1.2.2 155.1.2.1
155.1.3.1
*If DSL card is an 8540 DSL card,
associated RTU will not have an IP address.
DSL Routing Table
Host/Net Subnet Mask
1) 155.1.3.4
255.255.255.255
2) 155.1.3.4
255.255.255.255
3) 155.1.3.6
255.255.255.255
4) 155.1.3.6
255.255.255.255
With no input filtering on the DSL ports, ES2 can successfully send traffic to the
NSP identifying itself as ES1 (155.1.3.4).
Now, consider that the following filter rules are applied to s1d:
IP Address Subnet Mask
155.1.3.6 255.255.255.255
Default —
With these filter rules active on s1d, when ES2 tries to send packets to ISP1, the
filter on the DSL card blocks the packets from being forwarded, because only
packets with a source IP address of 155.1.3.6 are forwarded.
November 1997
DSL Card*
RTU 1*
s1c
135.1.3.3
155.1.3.2
RTU 2*
s1d
135.1.3.5
8540 DSL 8546 DSL
Card Next-Hop Card Next-Hop
Address Address
155.1.3.1 155.1.3.1
s1c 135.1.3.3
155.1.3.1 155.1.3.1
s1d 135.1.3.5
Source/Destination
Source
—
ES1
155.1.3.4
ES2
155.1.3.4
ES2 spoofing
ES1's address
S/D (Source/
Destination)
src (source)
dst (destination)
src (source)
dst (destination)
97-15477-02
Action
Forward
Discard
8000-A2-GB21-20