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RE: Cisco filter question
From: Owen DeLong <owen () delong com>
Date: Fri, 22 Aug 2003 10:29:36 -0700


Because your acl matches echo reply and the packet is echo request.

Owen


--On Friday, August 22, 2003 10:02 AM -0700 Michel Py <michel () arneill-py sacramento ca us> wrote:


Instead of:
set interface Null0

Use: set ip next-hop 10.255.255.254

_and_
ip route 10.255.255.254 255.255.255.255 Null0 name BLACKHOLE

Michel.

-----Original Message-----
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu] On Behalf Of
Geo. Sent: Friday, August 22, 2003 9:17 AM
To: nanog () merit edu
Subject: Cisco filter question


Perhaps one of you router experts can answer this question. When using
the cisco specified filter

 access-list 199 permit icmp any any echo
    access-list 199 permit icmp any any echo-reply

    route-map nachi-worm permit 10
      ! --- match ICMP echo requests and replies (type 0 & 8)
      match ip address 199

      ! --- match 92 bytes sized packets
      match length 92 92

      ! --- drop the packet
      set interface Null0


    interface <incoming-interface>
      ! --- it is recommended to disable unreachables
      no ip unreachables

      ! --- if not using CEF, enabling ip route-cache flow is recommended
      ip route-cache policy

      ! --- apply Policy Based Routing to the interface
      ip policy route-map nachi-worm

why would it not stop this packet

15 1203.125000 0003E3956600 AMERIC6625D4 ICMP Echo: From 216.144.20.69 To
216.144.00.27 216.144.20.69 216.144.0.27 IP  FRAME: Base frame properties
    FRAME: Time of capture = 8/22/2003 11:54:16.859
    FRAME: Time delta from previous physical frame: 0 microseconds
    FRAME: Frame number: 15
    FRAME: Total frame length: 106 bytes
    FRAME: Capture frame length: 106 bytes
    FRAME: Frame data: Number of data bytes remaining = 106 (0x006A)
ETHERNET: ETYPE = 0x0800 : Protocol = IP:  DOD Internet Protocol
    ETHERNET: Destination address : 00C0B76625D4
        ETHERNET: .......0 = Individual address
        ETHERNET: ......0. = Universally administered address
    ETHERNET: Source address : 0003E3956600
        ETHERNET: .......0 = No routing information present
        ETHERNET: ......0. = Universally administered address
    ETHERNET: Frame Length : 106 (0x006A)
    ETHERNET: Ethernet Type : 0x0800 (IP:  DOD Internet Protocol)
    ETHERNET: Ethernet Data: Number of data bytes remaining = 92 (0x005C)
IP: ID = 0x848; Proto = ICMP; Len: 92
    IP: Version = 4 (0x4)
    IP: Header Length = 20 (0x14)
    IP: Precedence = Routine
    IP: Type of Service = Normal Service
    IP: Total Length = 92 (0x5C)
    IP: Identification = 2120 (0x848)
    IP: Flags Summary = 0 (0x0)
        IP: .......0 = Last fragment in datagram
        IP: ......0. = May fragment datagram if necessary
    IP: Fragment Offset = 0 (0x0) bytes
    IP: Time to Live = 124 (0x7C)
    IP: Protocol = ICMP - Internet Control Message
    IP: Checksum = 0x70D8
    IP: Source Address = 216.144.20.69
    IP: Destination Address = 216.144.0.27
    IP: Data: Number of data bytes remaining = 72 (0x0048)
ICMP: Echo: From 216.144.20.69 To 216.144.00.27
    ICMP: Packet Type = Echo
    ICMP: Echo Code = 0 (0x0)
    ICMP: Checksum = 0x82AA
    ICMP: Identifier = 512 (0x200)
    ICMP: Sequence Number = 7680 (0x1E00)
    ICMP: Data: Number of data bytes remaining = 64 (0x0040)
00000:  00 C0 B7 66 25 D4 00 03 E3 95 66 00 08 00 45 00   .À·f%Ô..ã*f...E.
00010:  00 5C 08 48 00 00 7C 01 70 D8 D8 90 14 45 D8 90   .\.H..|.pØØ?.EØ?
00020:  00 1B 08 00 82 AA 02 00 1E 00 AA AA AA AA AA AA   ....'ª....ªªªªªª
00030:  AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA   ªªªªªªªªªªªªªªªª
00040:  AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA   ªªªªªªªªªªªªªªªª
00050:  AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA   ªªªªªªªªªªªªªªªª
00060:  AA AA AA AA AA AA AA AA AA AA                     ªªªªªªªªªª





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