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Showing posts from January 17, 2010

Context-Based Access Control (CBAC)

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IntroductionThe Context-Based Access Control (CBAC) feature of the Cisco IOS® Firewall Feature Set actively inspects the activity behind a firewall. CBAC specifies what traffic needs to be let in and what traffic needs to be let out by using access lists (in the same way that Cisco IOS uses access lists). However, CBAC access lists include ip inspect statements that allow the inspection of the protocol to make sure that it is not tampered with before the protocol goes to the systems behind the firewall.
PrerequisitesRequirementsThere are no specific requirements for this document.
Components UsedThis document is not restricted to specific software and hardware versions.
ConventionsFor more information on document conventions, refer to the Cisco Technical Tips Conventions.
Background InformationCBAC can also be used with Network Address Translation (NAT), but the configuration in this document deals primarily with pure inspection. If you perform NAT, your access …

Multicast VLAN Registration (MVR)

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IntroductionIn multicast VLAN networks, subscribers to a multicast group can exist in more than one VLAN. If the VLAN boundary restrictions in a network consist of Layer 2 switches, it might be necessary to replicate the multicast stream to the same group in different subnets, even if they are on the same physical network. Multicast VLAN Registration (MVR) routes packets received in a multicast source VLAN to one or more receive VLANs. Clients are in the receive VLANs and the multicast server is in the source VLAN. Multicast routing has to be disabled when MVR is enabled. Refer to the configuration guide at Understanding Multicast VLAN Registration for more information on MVR.
This document provides a simple topology: a stack of Catalyst 3750 Switches with multicast source/receivers connected to it, a working configuration, and output of commands to verify whether the MVR works or not when a stream is sending.
PrerequisitesRequirementsThere are no specific requi…

Multicast Routing Monitor (MRM)

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MRMMulticast Routing Monitor (MRM) facilitates automated fault detection in a large multicast routing infrastructure. MRM is designed to alert a network administrator of multicast routing problems near to real-time.
MRM has two components: MRM tester and MRM manager. MRM tester is a sender or receiver.
MRM is available in Cisco IOS Software Release 12.0(5)T and later. Only the MRM testers and managers need to be running the MRM-supported Cisco IOS version.

Test Sender Configuration
interface Ethernet0 ip mrm test-sender
Test Receiver Configuration
interface Ethernet0 ip mrm test-receiver
Test Manager Configuration
ip mrm manager test1 manager e0 group 239.1.1.1 senders 1 receivers 2 sender-list 1 access-list 1 permit 10.1.1.2 access-list 2 permit 10.1.4.2
Output from the show ip mrm manager command on Test Manager is shown here:
Test_Manager# show ip mrm manager Manager:test1/10.1.2.2 is not running Beacon interval/holdtime/ttl:60/86400/32 Group:239.1.…

Pragmatic General Multicast (PGM)

Pragmatic General Multicast (PGM) is a reliable multicast transport protocol for applications that require ordered, duplicate-free, multicast data delivery from multiple sources to multiple receivers. PGM guarantees that a receiver in the group either receives all data packets from transmissions and retransmissions or can detect unrecoverable data packet loss.

There are no PGM global commands. PGM is configured per interface with the ip pgm command. You must enable Multicast routing on the router with PIM on the interface.

c-BPDU(configuration BPDU) vs tcn-BPDU(topology change BPDU)

There are two types of BPDU's: configuration BPDU's (c-BPDU) and topology change BPDU's (tcn-BPDU).

Designated Bridges generate c-BPDU's. Root Ports and BLocked Ports listen for c-BPDU's.

c-BPDU's originate from the root bridge and flow out towards the edge of the spanning tree, c-BPDU's are re-generated at every bridging device that receives them.

tcn-BPDU's originate from root ports and flow towards the Root Bridge.

c-BPDU's are the heartbeat of the Spanning Tree,
tcn-BPDU's are the heart attack of the spanning tree.