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Page 186 / 998 Scroll up to view Page 181 - 185
Switching
Switch command reference
iMG/RG Software Reference Manual (Switching)
2-36
Description
This command displays the current mapping of user priority level to QOS egress queue
for the switch.
Switch Quality Of Service configuration
--------------------------------------------------------------------
Priority Map:
Addr | 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
-----------------------------------------------
00
| . . . . . . . . . . . . . . . . . . . .
20
| . . . . . . . . . . . . . . . . . . . .
40
| H H H H H H H H H H H H H H H H H H H H
60
| H H H H
--------------------------------------------------------------------
2.2.4.1.49 SWITCH SHOW QOS 802.1P
Syntax
SWITCH SHOW QOS 802.1P
Description
This command displays the current mapping of the switch egress queues with respect to
the 802.1p priority field value of the tag header of the an incoming tagged frame.
Example
--> switch show qos 802.1p
Tag Que Map:
Queue Range: 0-3
PID
|
0
1
2
3
4
5
6
7
---------------------------------------
QUEUE |
0
0
1
1
2
2
3
3
2.2.4.1.50 SWITCH SHOW QOS DSCP
Syntax
SWITCH SHOW QOS DSCP
Description
This command displays the current mapping of the switch egress queues respect the
TOS/DiffServ/Traffic class value in the IP header of the an incoming frame.
Example
--> switch show qos dscp
DSCPQue Map:
Queue Range: 0-3
DSCP
|
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
9
--------------------------------------------------------------------------------
00
|
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
20
|
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
40
|
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
60
|
3
3
3
3
Page 187 / 998
Overview
BRIDGE
2-37
iMG/RG Software Reference Manual (Switching)
2.3
BRIDGE
2.3.1
Overview
The Bridge module acts as an extension to the existing Layer 2 switch - providing connectivity between the
applications and services provided in the CPU and the devices connected to the LAN ports also provides sup-
port for virtual LANs in order to create multiple domains in which the packets are forwarded. The Bridge mod-
ule also provides standard interfaces for attachment to the system TCP/IP Stack allowing the termination of IP
frames belonging to a specific VLAN to a well defined IP interface.
A key point of interest here is that the port associated with the Bridge is not the Ethernet Port from the switch
- there is a single interface between the switch and the bridge, and then additional connections to the different
functions - such as the ADSL interface - or the IP interface.
2.3.2
Bridge Functional Description
2.3.2.1 Source MAC based forwarding
The source based MAC forwarding entries are unicast entries configured to forward packets on the specified
port that is configured for the MAC address, which matches the destination MAC address of the packet. They
are also used to restrict forwarding of packets to the ports specified in the entry if MAC address and source
port matches the source MAC address of the packet and the port on which packet is received.
The source based MAC entries (named also static unicast entries source based) can be created/deleted by the
user through. These entries have higher priority over the dynamic entries, meaning that the learned entry does
not overwrite the static unicast entry with the same MAC address.
A static unicast entry serves the following purpose in packet forwarding:
•
For a packet received from the port with its source MAC address and received port matching the static uni-
cast entry’s MAC address and the source port respectively, then the packet will be forwarded to the respec-
tive ports as specified by the entry’s destination mask;
•
For a packet received from a port with its source MAC address matching but withdifferent source port, the
packet will be discarded;
•
For a packet received from a port with its destination MAC address matching a static unicast entry, the
packet will be forwarded to the source port of the entry.
2.3.2.2 Destination MAC based forwarding
The destination based MAC forwarding entries are configured to forward packets to the ports specified in the
entry whose MAC address matches the destination MAC address of the packet. In the absence of a static uni-
cast entry or a dynamic entry, it provides the capability to forward unicast packets to the ports on which the
Page 188 / 998
BRIDGE
Bridge Functional Description
iMG/RG Software Reference Manual (Switching)
2-38
particular destination might be present. It is also used to create multicast entries and forward multicast packets
to all ports listening for that particular multicast address.
The destination based MAC entries (named also static unicast entries destination based) can be created/deleted
by the user.
For a specific MAC address, there can exist either a static unicast entries source based or a destination unicast
entries source based. However, a destination based MAC entry is updated to be of type static + dynamic if a
packet is received with the source MAC address matching the destination based MAC entry’s MAC address. In
that case, the source port field that was unused for destination based MAC entry type is updated to the source
port on which the MAC address is learnt.
A destination based MAC entry serves the following purpose in packet forwarding:
•
For a packet received from a port with its destination MAC address matching a destination based MAC
entry entry’s MAC address, the packet will be forwarded to the ports as specified by the entry’s destination
mask;
•
For a packet received from a port with its destination MAC address matching a destination based MAC
entry + dynamic entry’s MAC address, the packet will be forwarded to the source port specified in the
entry;
2.3.2.3 Port based forwarding
Port based forwarding is an additional mechanism to forward
packets based on the port on which the packets
are received. This forwarding applies to all packets received, irrespective of their source and destination MAC
addresses.
Port based forwarding is the first level of forwarding applied to the received packets. The destination mask is
set to the forwarding mask of the port on which the packets are received. It serves the following purpose in
packet forwarding:
•
If a source based MAC entry or a dynamic MAC entry matching the destination MAC address is found, the
packet is forwarded to the specified source port only if the port exists in the port forwarding mask of the
port on which packet is received.
•
If a source based MAC entry matching the source MAC address is found, the packet is forwarded to all the
ports that exist in the destination mask as well as the port forwarding mask of the port on which packet is
received.
•
If a destination based MAC entry, matching the destination MAC address is found, the packet is forwarded
to the all the ports that exist in the destination mask of the entry as well as the port forwarding mask of the
port on which packet is received.
2.3.2.4 Traffic Prioritization
The bridge module provides support for traffic prioritization in conformance to the IEEE 802.1p specifications.
Page 189 / 998
Bridge Functional Description
BRIDGE
2-39
iMG/RG Software Reference Manual (Switching)
To regenerate priority mapping, it can be configured for each port such that, whenever a tagged packet is
received with a specified priority in the tag header, it is mapped to the corresponding regenerated priority and
the tag header is reset with the new priority.
Additionally, it can be configured to prioritize traffic based on certain traffic classes defined for each outgoing
port. Based on these mappings, the regenerated priority is mapped to the corresponding traffic class priority,
which is set as the system buffer priority such that the transmitted packets are appropriately prioritized by the
lower layers. The actual priority transmission of packets is performed by the Scheduler device. The scheduler
device transmits packets with highest priority first, followed by lower priority packets and finally the lowest pri-
ority packets.
Priority handling has the following effect on the forwarding path:
•
If the packet receive is untagged, assign the default priority of the port on which packet is received else
obtain the user priority from the tag header.
•
Maps the user priority to the regenerated priority based on the configuration of the received port.
•
If the packet is forwarded as tagged, it sets the regenerated priority in the tag header.
•
If traffic class mapping is enabled, it obtains the traffic class mapping based on the configuration of the outgo-
ing port and sets the priority in the system buffer.
2.3.2.5 Multicast Traffic
The system supports configuration and handling of multicast MAC forwarding entries, forward all and forward
unregistered entries. Forwarding of the multicast packets is done based on these entries. By default, multicast
traffic is forwarded to all ports. With the addition of support for IGMP snooping in the Bridge, multicast for-
warding is further optimized, by intelligent forwarding of multicast traffic in the network..
Additionally, the system provides configuration of forward all and forward unregistered ports.
Forward all ports are the ports to which all multicast data will always be forwarded. Forward unregistered ports
are the ports to which the multicast data needs to be forwarded, for which there exists no multicast filtering
entry.
2.3.2.6 Learning
Learning is carried out for each unicast packet received by the bridge. Based on the source MAC address and
the source port on which the packet is received, the bridge updates it forwarding database so that whenever a
packet with destination as the learnt MAC address is received, it sends it to the appropriate port on which it
had learnt that MAC address.
The entries are aged out with a periodicity of filter age time configured by the user.
The entries are learnt only on those ports that are in either learning or forwarding state.
Learning is carried out in the following manner:
Page 190 / 998
BRIDGE
Functional Differences in Product Categories
iMG/RG Software Reference Manual (Switching)
2-40
•
If there already exists an Dynamic entry with MAC address that matches the source MAC address, it
updates the last seen time and the source port for the entry.
•
If there exists a Static entry with MAC address that matches the source MAC address, it updates entry’s
source port field with the received port.
2.3.3
Functional Differences in Product Categories
A key difference between the different models is the incorporation of a VLAN Aware Bridge implementation.
As a part of this enhancement - additional flexibility was added to support MAC Filtering. Note that some com-
mands described here - presume support for multiple VLANs w/in the Bridge. For more information on the
VLAN specific functions - please see the VLAN section.
It is not often that a user would need to manipulate the forwarding databases. This capability is there...but not
anticipated to be widely utilized.
Note 1) On these devices - Multicast traffic is forwarded to all ports with no options for filtering/restriction.
Note 2) For these devices there is only one Forwarding DataBase - the DefaultFDB - for other devices - it is
possible to create multiple Forwarding Databases via the Bridge Add VLAN command.
Note 3) Dynamic Destination MAC based forwarding is the only mechanism supported here. The Bridge learns
which MAC addresses come from which ports - and forwards packets with that MAC as a Destination MAC to
those ports. There is no support for static configuration of
MAC Addresses.
2.3.4
Bridge command reference
This section describes the commands available for Bridge.
TABLE 2-3
Functional Mapping for Bridge
Commands
Fiber
A
Fiber
B
Fiber
C
Fiber
D
Fiber
E
Modular
ADSL
A
ADSL
B
ADSL
C
Port based forwarding
X
X
X
X
X
X
Traffic Prioritization
X
X
X
X
X
X
Multicast Traffic
1
X
1
X
X
X
1
X
X
Learning
X
X
X
X
X
X
X
X
X

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