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Forum Replies

  1. First step to protect against DoS and DDoS attacks.

    Further ones may include RTBH, prefix-lists denying the bogon and spoofed prefixes, CoPP on the backplane and rate-limiters.

  2. Hi Rene,

    I got the uRPF function clearly but want to know how uRPF prevents these spoofing attacks. Actually want want to know “spoofing attacks” Scenario.Sorry for bothering you again n Again .Thanks


  3. HI rene, great explanation as usual !

    Assuming the attacker’s goal is to access the “target devices” behind R1 ( that is to establish a TCP connection with return path). The attacker that has the spoofed Source Address can indeed reach the target hosts, however when the “target host” replies , R1 will forward the reply to the legitimate device holding the “true” source network ( in your example). So in any case the attacker cannot "access " its victim, but rather send them packet with no response right ?

  4. Hello Paul

    It really depends on the platform you are using. Higher end platforms (6500/6800 with the appropriate supervisor as well as Nexus platforms for example) will support uRFP occurring in hardware thus providing for fast checking and no taxing of other resources.

    If you specify an access list, you are essentially telling the router which range of addresses you want checked. So if a source is in the access list specified, the uRPF takes place. If it is not specified in the access list, then the uRPF check is bypassed.

    I hope this has been helpful!


  5. Hi Rene,

    I have couple of questions.

    1. Can i enable uRPF on both ingress & egress interface?
    2. I read somewhere that uRPF rely on CEF table. So we should enable CEF as well to work with uRPF?
    3. How uRPF work with equal & unequal cost load balancing? Like OSPF & EIGRP?


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