Spoofing
One of the most popular ISDN techniques is called spoofing, which is where the router responds to keepalive packets instead of sending them to the remote party. If the spoofing is "up," the protocol layer is reporting up, as shown in Example 11-1. In order for any interface to report the protocol layer up, the other party must respond to keepalives, but in spoofing, the router itself responds to keepalives. Spoofing is also part of the troubleshooting technique to check the status of the dialer interface. Even when the router does not make a call, the dialer shows a spoofing state.
Example 11-1 show interfaces dialer 1 Command Output Reveals Dialer1 is up (spoofing), line protocol is up (spoofing)
804-isdn# show interfaces dialer 1
Dialerl is up (spoofing), line protocol is up (spoofing) Hardware is Unknown
Interface is unnumbered. Using address of Ethernet0 (151.70.209.81) MTU 1500 bytes, BW 128 Kbit, DLY 20000 usee, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) DTR is pulsed for 1 seconds on reset Last input never, output never, output hang never Last clearing of "show interface" counters never
Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/0/16 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 112555 packets input, 102607119 bytes 77225 packets output, 9186472 bytes
If you monitor the 5 minute input rate and 5 minute output rate counters in Example 111, you don't see any activity. The spoofing only imitates an active state of the dialer, but this does not mean that the router is connected, or makes a call. This is the cost-saving effect of the spoofing because the router is not connected and there is no charge from the local provider. To clarify, the router makes a call only if the DDR conditions are met.
Continue reading here: Step 1Configuring the Dialer Interface
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