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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 36 Configuring Denial of Service Protection
DoS Protection Configuration Guidelines and Restrictions
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When using QoS ACLs to limit the rate of packets, note the following information:
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The QoS ACL must specify the traffic flow to be rate limited.
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When adding a QoS ACL to limit the rate of packets to an interface that already has a QoS ACL
configured, you can perform one of the following:
* Merge the rate-limiting ACL with the existing QoS ACL.
* Define a separate class that matches the DoS ACL and tie the class to the policy map.
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QoS ACLs need to be configured on all external interfaces that require protection. Use the
interface range command to configure an ACL on multiple interfaces.
•
The CPU rate limiters limit the traffic in aggregate only and do not distinguish between good and
bad packets.
•
The following FIB rate-limiting usage guidelines apply:
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FIB rate limiting does not limit the rate of broadcast or some multicast traffic in hardware.
The PFC3 has separate multicast rate limiters. The Supervisor Engine 2 does not have separate
multicast rate limiters.
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FIB rate limiting does not differentiate between legitimate and illegitimate traffic (for example,
tunnels, Telnet).
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FIB rate limiting applies aggregate rate limiting and not per-flow rate limiting.
PFC3
When configuring DoS protection on systems configured with a PFC3, follow these CPU rate limiter
guidelines and restrictions:
Note
For the CoPP guidelines and restrictions, see the
“CoPP Configuration Guidelines and Restrictions”
section on page 36-28
.
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Do not use these rate limiters if multicast is enabled in systems configured with a PFC3A:
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TTL failure
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MTU failure
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These rate limiters are supported only in PFC3B or PFC3BXL mode:
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Unicast IP options
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Multicast IP options
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These are Layer 2 rate limiters:
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Layer 2 PDUs
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Layer 2 protocol tunneling
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Layer 2 Multicast IGMP
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There are eight Layer 3 registers and two Layer 2 registers that can be used as CPU rate limiters.
•
Do not use the CEF receive limiter if CoPP is being used. The CEF receive limiter will override the
CoPP traffic.
•
Rate limiters override the CoPP traffic.