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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Cisco - ip verify unicast reverse-path
This command has been mentioned numerous times during the DDoS discussion. I, for one, don't have a good idea of how it works. Perhaps someone can enlighten us? Cisco's web site certainly doesn't do much to help the situation. I found it mentioned in the guide (not the reference) for the Cat 6000 (http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/ios127xe/config/secure.htm#xtocid598314) - no description of syntax, let alone what it does. And then there is http://www.cisco.com/warp/public/707/newsflash.html. It says that the RPF check is based on CEF. I'm not familiar with CEF and want to clarify something about unicast RPF. If the source address of a packet arrived on an interface that would not be the preferred route for that address but is one of the less-preferred routes would the packet get dropped? If, as I hope, it would not, I don't understand the argument that it doesn't work for multi-homed connections. Such systems should be advertising their routes over all connections - thus the routes should appear on all paths outbound from the multi-homed systems (less any long prefix filtering being done by the upstreams). Another issue is why has Cisco made this such a stealth feature? Is it still buggy? Are the side-effects of using it so negative that hardly anyone can use it? If any such speculation is true, the folks advocating the use of this feature should also be pointing out the downside. Tony Rall
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