Multicast - DR and Querying Router

Today I would like to share some important concept about Multicast PIM-Sparse Mode DR and querier elections in PIM and role of them.

As we all know, IGMP has IGMP versions v1, v2 and v3.

In every version, The concept and role is bit different.

First let’s see about roles.

Roles:

Querier – Querying Router tasks is to send IGMP query message to LAN network , ensuring that is any one is still interested to join this multicast stream. As any of host will send a leave message in IGMPv2 , the querier router will send out query addressing to 224.0.0.1 (all multicast host) is anyone else would like to access this stream. If any host sends membership report for particular group. Then It will continue its task, If not It will discontinue.

DR – The DR is responsible for sending Join/Prune messages to the RP. Another role of DR is it sends a source-register message to the rendezvous point, on behalf of a source.

Let’s come to concept –

Many times confusions happens that querier and DR is one router only or what is use of DR?

• In IGMP v1 – Both tasks are performed by one router.
• In IGMP v2 - 
• At start up each router sends a query message to the all 224.0.0.1 from its own interface address. The router with the lowest ip address is elected IGMP querier.

                      AND

• Among all PIM-SM enabled router, Highest IP address will win DR selection, One more criteria can change this election, interface DR priority. But by default priority will be 1 for every interface, you can change priority under interface. Then highest priority will win DR election. Then that particular router will be responsible to send your join messages to RP and ensure about your communication.

This concept mainly applies, in shared LAN segment with more PIM enabled routers. You need to make sure that who should be concern router for DR, to handle join messages.

                                      Otherwise many times, by mistakenly any router in LAN segment enabled with PIM can be DR due to by default selection parameters and will handle your join messages coming from LAN hosts. Which will disturb your Multicast flow, since that another router will not have path to reach RP, So make sure in shared LAN environment you configured proper DR in all PIM enabled router.

The Designated Router in Detail -

When multiple routers are connected to a multi-access network (for example, an Ethernet) one of them must be selected to act as the designated router (DR) for a given period of time. The DR is responsible for sending Join/Prune messages to the RP. To elect the DR, each PIM router on the network examines the received Hello messages and compares its IP address with those of its neighbors. The router with the highest address is the DR. But highest priority can overcome it. 

Configuration :

MP1800(config-if-fastethernet0)#ip pim dr-priority 200 ?   

To check more in Router, Plz use show ip igmp interface (int)(Cisco command) , It will show you querier Router IP address and DR router detail.  In Maipu Routers "show ip igmp interface" will show you querier router IP address and "show ip pim neighbor detail" will show you detail about DR. 

It will show details about querying router and DR to us. 

Hope this information will help you for more understanding about DR and querying router in PIM sparse mode. For more information you can refer RFC 2236.

Hope this post is informative for you.

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Thanks for reading… 

Link Aggregation - Maipu and Cisco

Today we will discuss about Link aggregation, This is very important topic in switching. This is many times used in Enterprises network for trunking. Basically this will help to bind several physical links together to form a logical link and it can be used to increase link bandwidth for trunk. Meanwhile, each aggregation member link can achieve dynamic backup with each other to provide higher connection reliability.

This section describes the concept of the link aggregation. Main contents:

• Terms of the link aggregation
• Functions of the link aggregation
• LACP protocol

Terms of the Link Aggregation

Link aggregation: multiple physical links are bound together to form a logical link, which expands the link bandwidth. At the same time, the member links of the aggregation are dynamic backup mutually. It provides higher reliability.

• LAC: Link Aggregation Control
• LACP: Link Aggregation Control Protocol, defined in IEEE802.3ad.
• LACPDU: Link Aggregation Control Protocol Data Unit.
• LAG: Link Aggregation Group.
• LAG ID: Link Aggregation Group Identifier.
• Key: 16-bit integer variable, for describing the aggregation capability of a port. It is composed of rate, duplex, and administrative key (aggregation group ID).
• Administrative Key: The key used by the administrator for setting.
• Operational Key: The key reflecting the port aggregation capability.

Functions of the Link Aggregation

The link aggregation is a aggregation group composed of multiple ports. The upper layer entities using the link aggregation service regard the multiple physical links in the same aggregation group as a logical link. The function of the link aggregation is to share the in/out load in each member port to increase the link bandwidth. At the same time, member ports of the aggregation group are dynamic backup mutually. It provides higher reliability.

LACP Protocol

IEEE802.3ad-based LACP is a protocol for implementing the link dynamic aggregation. The LACP protocol communicates with the opposite end through the Link Aggregation Control Protocol Data Unit (LACPDU). After the LACP protocol of a port is enabled, the port advertises the system priority, system MAC address, port priority, port number, and the operation key to the opposite end by sending LACPDU. After the opposite end receives the information, compare the information with the information saved in other ports to select port to aggregate. As a result, the two parties can agree with each other on joining or exiting a dynamic aggregation group. The operation key is a configuration combination generated by the LACP protocol according to the port configuration (rate, duplex, administrative key).

Classification of Link Aggregation

The link aggregation can be classified into two types according to the aggregation mode:

• Manual aggregation
•  LACP protocol aggregation

Below are configuration examples for both modes.

Configuration for Link Aggregation

Topology

LAC configuration

As figure above, ports 0/1-0/3 between two switches connect with each other. Local switch switch1 aggregates peer switch switch2; three ports of each side participate in the aggregation. Suppose that the numbers of the ports that participate in the aggregation at the two sides are all 0/1-0/3.

Mode 1: Manual Aggregation

switch1 configuration:

Command	Description
switch (config)#link-aggregation 1 mode manual	Create manual aggregation group 1
switch (config)#port 0/1-0/3	Enter the port mode
switch (config-port-range)#link-aggregation 1 manual	Add a port into aggregation group in manual mode

switch2 configuration:

Command	Description
switch (config)#link-aggregation 1 mode manual	Create manual aggregation group 1
switch (config)#port 0/1-0/3	Enter the port mode
switch (config-port-range)#link-aggregation 1 manual	Add a port into an aggregation group in manual mode

Mode 2: Protocol Aggregation

switch1 configuration

Command	Description
switch (config)#link-aggregation 1 mode lacp	Create protocol aggregation group 1
switch (config)#port 0/1-0/3	Enter the port mode
switch (config-port-range)#link-aggregation 1 active	Add a port into an aggregation group in protocol mode

switch2 configuration:

Command	Description
switch (config)#link-aggregation 1 mode lacp	Create protocol aggregation group 1
switch (config)#port 0/1-0/3	Enter the port mode
switch (config-port-range)#link-aggregation 1 active	Add a port into an aggregation group in protocol mode

Monitoring Commands

View Commands:

Command	Description
show link-aggregation group [agg-id]	Display the aggregation information of a specified aggregation group
show link-aggregation port [port_no]	Display the aggregation information of a port

Debugging Commands

Command	Description
(no) debug lac [pdu [rx|tx] | machine | event ] [port port-no]	Enable the debugging switch of the information about link aggregating process.

Hope this information will help you for understanding of Link aggregation concept and configuration in Maipu Switches for Cisco it’s same. Cisco is having PAGP propriety protocol for Link aggregation.

Port Aggregation Protocol (PAGP)

• Cisco Proprietary
• Port Modes : Auto , Desirable , On

If Both side you set as a Auto mode then it will not become Ether Channel

• Auto Means : It will say u want to be a Ether channel
• Desirable Mode: It will u r Ether channel the I will be.
• On: No Negotiating -- He will be only Ether channel and Destination Switch should be configured as a Ether channel. [ Better One ]

 PagP Configuration Example :-

SwitchA(config)# int range fastethernet 0/23 - 24

SwitchA(config- if)# channel-protocol PagP

SwitchA(config- if)# channel-group 1 mode desirable

SwitchB(config)# int range fastethernet 0/23 - 24

SwitchB(config- if)# channel-protocol PagP

SwitchB(config- if)# channel-group 1 mode auto

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