Access List-Based RBSCP
Access List-Based RBSCP
Last Updated: May 14, 2011
The Access List-Based Rate-Based Satellite Control Protocol (RBSCP) feature allows you to selectively apply the TCP ACK splitting feature of RBSCP to any outgoing interface. The result is reduced effect of long latencies over a satellite link. Access List-Based RBSCP has no tunneling or queueing overhead that is associated with RBSCP tunnels. Additional benefits include more interoperability with other Cisco IOS features (such as TCP/IP header compresssion, DMVPN, and QoS) because the TCP and Stream Control Transmission Protocol (SCTP) packets are no longer encapsulated with an RBSCP/IP header. This feature works on process switched forwarding, fast switching, or Cisco Express Forwarding (CEF).
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
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.
Prerequisites for Access List-Based RBSCP
This document assumes that you already understand how to configure an IP access list and have one configured.
Restrictions for Access List-Based RBSCP
Information About Access List-Based RBSCP
Benefits of Access List-Based RBSCP
The Access List-Based Rate-Based Satellite Control Protocol (RBSCP) feature provides the following benefits:
Rate-Based Satellite Control Protocol
Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model. For instructions on how to implement RBSCP over a tunnel, see the âImplementing Tunnelsâ chapter of the Interface and Hardware Component Configuration Guide .
The TCP ACK splitting capability of RBSCP can be implemented without a tunnel, by using an IP access list, as shown in the figure below. The TCP ACK splitting occurs at the outgoing interface between the router and the internal network or Internet. It does not occur over the link to the satellite.
TCP ACK Splitting
TCP ACK splitting is a software technique to improve performance for clear-text TCP traffic using acknowledgment (ACK) splitting, in which a number of additional TCP ACKs are generated for each TCP ACK received. TCP ACK splitting causes TCP to open the congestion window more quickly than usual, thus decreasing the effect of long latencies. TCP will generally open the congestion window by one maximum transmission unit (MTU) for each TCP ACK received. Opening the congestion window results in increased bandwidth becoming available. Configure this feature only when the satellite link is not using all the available bandwidth. Encrypted traffic cannot use TCP ACK splitting.
The size argument in the ip rbscp ack-splitcommand determines how many TCP ACKs are generated from the incoming TCP ACK, as shown in the figure below.
If n ACKs are configured and M is the cumulative ACK point of the original TCP ACK, the resulting TCP ACKs exiting the router will have the following cumulative ACK points:
M-n+1, M-n+2, M-n+3,...M
For example, if the size argument is set to 5, and the access list permits a TCP ACK with a cumulative ACK acknowledging bytes to 1000, then the resulting TCP ACKs exiting the router will have the following cumulative ACK points:
TCP ACK (996) (1000-5+1)
TCP ACK (997) (1000-5+2)
TCP ACK (998) (1000-5+3)
TCP ACK (999) (1000-5+4)
TCP ACK (1000) (1000-5+5)
Access List-Based RBSCP Functionality
The Access List-Based RBSCP feature will accept a numbered or named, standard or extended IP access list. The access list controls which packets are subject to TCP ACK splitting. That is, the feature is applied to packets that a permit statement allows; the feature is not applied to packets that a deny statement filters.
An instance of this feature consists of an access list and an ACK split value. An ACK split value of 0 or 1 indicates that this feature is disabled (that is, no ACK split will be done). The ACK split value range is 0 through 32.
An interface can use only one instance of this feature at a time. Each instance of this feature can be used on multiple interfaces.
If you configure this feature but it refers to a nonexistent access list, this is interpreted as having an access list that denies all traffic from being processed by the access list-based RBSCP feature, so the feature is essentially disabled and the traffic goes through the normal switching path.
If both an RBSCP tunnel and an instance of the Access List-Based RBSCP feature are enabled along a routing or switching path, the TCP ACKs detunneled from the RBSCP tunnel will be ACK split according to the tunnel configuration and the Access List-Based RBSCP split parameters on the outgoing interface are effectively disabled.
How to Configure Access List-Based RBSCP
Use RBSCP Selectively by Applying an Access List
This task illustrates how to apply the feature to an interface, and presumes that an access list is already configured. Perform this task by applying the access list on the router interface that is facing the internal network, not the satellite network.
5. Although it is not required, you should repeat this task on the router that is on the other side of the satellite, on the outgoing interface facing the network, not the satellite. Use a different access list.
Configuration Examples for Access List-Based RBSCP
Example Access List-Based RBSCP
In the following example, access list 101 performs TCP ACK splitting on packets going out FastEthernet interface 1/1 from a source at 126.96.36.199 to a destination at 188.8.131.52:
! version 12.4 no service pad service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname IOSACL-72b ! boot-start-marker boot-end-marker ! enable password lab ! no aaa new-model ! resource policy ! ip cef ! interface Ethernet0/0 no ip address shutdown duplex auto no cdp enable ! interface GigabitEthernet0/0 no ip address shutdown duplex full speed 1000 media-type gbic negotiation auto no cdp enable ! interface FastEthernet1/0 ip address 184.108.40.206 255.255.255.0 duplex half no cdp enable ! interface FastEthernet1/1 ip address 220.127.116.11 255.255.255.0 ip rbscp ack-split 4 101 out duplex half no cdp enable ! interface FastEthernet2/0 no ip address shutdown duplex half no cdp enable ! interface Serial3/0 no ip address shutdown serial restart-delay 0 ! interface Serial3/1 no ip address shutdown serial restart-delay 0 no cdp enable ! interface Serial3/2 no ip address shutdown serial restart-delay 0 no cdp enable ! interface Serial3/3 no ip address shutdown serial restart-delay 0 no cdp enable ! interface FastEthernet4/0 no ip address shutdown duplex auto speed auto no cdp enable ! interface FastEthernet4/1 no ip address shutdown duplex auto speed auto no cdp enable ! router eigrp 100 network 18.104.22.168 network 22.214.171.124 auto-summary ! no ip http server no ip http secure-server ! logging alarm informational access-list 101 permit tcp host 126.96.36.199 host 188.8.131.52 dialer-list 1 protocol ip permit ! control-plane ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! end
Feature Information for Access List-Based RBSCP
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.
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.