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The ACL IP Options Selective Drop feature allows Cisco routers to filter packets containing IP options or to mitigate the effects of IP options on a router or downstream routers by dropping these packets or ignoring the processing of the IP options.
Resource Reservation Protocol (RSVP) (Multiprotocol Label Switching traffic engineering [MPLS TE]), Internet Group Management Protocol Version 2 (IGMPv2), and other protocols that use IP options packets may not function in drop or ignore modes.
The ACL IP Options Selective Drop feature allows a router to filter IP options packets, thereby mitigating the effects of these packets on a router and downstream routers, and perform the following actions:
Drop all IP options packets that it receives and prevent options from going deeper into the network.
Ignore IP options packets destined for the router and treat them as if they had no IP options.
For many users, dropping the packets is the best solution. However, in environments in which some IP options may be legitimate, reducing the load that the packets present on the routers is sufficient. Therefore, users may prefer to skip options processing on the router and forward the packet as though it were pure IP.
Drop mode filters packets from the network and relieves downstream routers and hosts of the load from options packets.
Drop mode minimizes loads to the Route Processor (RP) for options that require RP processing on distributed systems. Previously, the packets were always routed to or processed by the RP CPU. Now, the ignore and drop forms prevent the packets from impacting the RP performance.
This section describes how to configure the ACL IP Options Selective Drop feature.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
enable Example: |
Enables privileged EXEC mode.
|
| Step 2 |
configure terminal Example: |
Enters global configuration mode. |
| Step 3 |
ip options {drop | ignore } Example: |
Drops or ignores IP options packets that are sent to the router. |
| Step 4 |
exit Example: |
Returns to privileged EXEC mode. |
| Step 5 |
show ip traffic Example: |
(Optional) Displays statistics about IP traffic. |
The following example shows how to configure the router (and downstream routers) to drop all options packets that enter the network:
Router(config)# ip options drop
% Warning:RSVP and other protocols that use IP Options packets may not function in drop or ignore modes.
endThe following sample output is displayed after using the ip options drop command:
Router# show ip traffic
IP statistics:
Rcvd: 428 total, 323 local destination
0 format errors, 0 checksum errors, 0 bad hop count
0 unknown protocol, 0 not a gateway
0 security failures, 0 bad options, 0 with options
Opts: 0 end, 0 nop, 0 basic security, 0 loose source route
0 timestamp, 0 extended security, 0 record route
0 stream ID, 0 strict source route, 0 alert, 0 cipso, 0 ump
0 other, 30 ignored
Frags: 0 reassembled, 0 timeouts, 0 couldn't reassemble
0 fragmented, 0 fragments, 0 couldn't fragment
Bcast: 0 received, 0 sent
Mcast: 323 received, 809 sent
Sent: 809 generated, 591 forwarded
Drop: 0 encapsulation failed, 0 unresolved, 0 no adjacency
0 no route, 0 unicast RPF, 0 forced drop, 0 unsupported-addr
0 options denied, 0 source IP address zeroThe following sections provide references related to IP access lists.
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Related Topic |
Document Title |
|---|---|
|
Configuring IP access lists |
"Creating an IP Access List and Applying It to an Interface" |
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Cisco IOS commands |
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IP access list commands |
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Description |
Link |
|---|---|
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The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
ACL IP Options Selective Drop |
Cisco IOS XE Release 2.1 |
The ACL IP Options Selective Drop feature allows Cisco routers to filter packets containing IP options or to mitigate the effects of IP options on a router or downstream routers by dropping these packets or ignoring the processing of the IP options. This feature was introduced on Cisco ASR 1000 Series Aggregation Services Routers. The following command was introduced: ip options . |
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