Smart-Link、Monitor-Link
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definition
Smart-link : also called backup link. A Smart-link consists of two interfaces, one of which acts as a backup for the other. Smart Link is often used in dual uplink networking, providing reliable and efficient backup and fast switching mechanisms.
Monitor Link is an interface linkage solution. It monitors the uplink interface of the device, and triggers the change of the Up/Down state of the downlink interface according to the change of its Up/Down state, thereby triggering the topology protocol on the downstream device to switch the link.
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Basic Principles of Smart-Link
Taking the network described in Figure 1 as an example, the basic principle of Smart Link operation is introduced according to the process of link normal -> link failure -> link recovery.
Figure 1 Schematic diagram of Smart Link
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How the link works
The Smart Link group on SwitchD includes Interface1 and Interface2, where Interface1 is the master interface and Interface2 is the slave interface. When both uplinks are normal, the primary interface is in the forwarding state, and the link it is on is the active link, and the secondary interface is in the standby state, and the link it is on is the backup link. As shown in Figure 2, data is transmitted along the main link, and there are no loops in the network to avoid broadcast storms.
Figure 2 Schematic diagram of traffic when the link is working normally
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Principles of Link Fault Handling
As shown in Figure 3, when the primary link of SwitchD fails, the primary interface Interface1 switches to the standby state, and the secondary interface Interface2 switches to the forwarding state. At this time, the MAC address forwarding entries and ARP entries on the relevant devices in the network are no longer applicable, and a mechanism for updating MAC and ARP needs to be provided. There are currently two update mechanisms.
Figure 3 Schematic diagram of uplink traffic when the main link fails
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Notify the device to update entries through Flush packets
This method is applicable to scenarios where upstream devices (SwitchA, SwitchB, and SwitchC in Figure 3) support the Smart Link function. To implement fast link switching, you need to enable the function of sending Flush packets on SwitchD, and enable the function of receiving and processing Flush packets on all interfaces on the upstream device that are on dual uplinks.
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After SwitchD performs link switching, it sends Flush packets from the new active link, that is, through Interface2.
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When the upstream device receives the Flush packet, it judges whether the sending control VLAN of the Flush packet is in the receiving control VLAN list configured on the interface receiving the packet. If it is not in the receiving control VLAN list, the device does not process the Flush packet and forwards it directly; if it is in the receiving control VLAN list, the device will process the received Flush packet, and then perform MAC address forwarding entry and ARP entry Refresh operation.
Afterwards, if SwitchA receives a data packet destined for SwitchD, it forwards it according to the updated MAC address forwarding entry or ARP entry.
Automatically update entries through traffic
This method is suitable for interconnecting with devices that do not support the Smart Link function (including devices from other manufacturers), and needs to be triggered by uplink traffic.
As shown in Figure 4, if there is no upstream traffic from SwitchD to trigger the update of SwitchA's MAC and ARP entries, then when SwitchA receives a data packet whose destination device is SwitchD, SwitchA will still forward it through Interface3. When the packets cannot reach SwitchD, traffic will be lost until its MAC or ARP entries automatically age out.
Figure 4 Schematic diagram of downlink traffic when the main link fails
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As shown in Figure 5, after the link fails, the MAC and ARP entries learned by Interface1 will be deleted. If SwitchD has uplink traffic to send, it needs to re-broadcast the ARP packet before the traffic can be sent out. When the uplink traffic reaches SwitchA through Interface4, SwitchA will update its MAC and ARP entries. Then, when SwitchA receives a data packet whose destination device is SwitchD, SwitchA will forward it through Interface4, and the packet can be SwitchD is reached via SwitchC.
Figure 5 Schematic diagram of downlink traffic when the main link fails
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The mechanism of notifying the device to update through the Flush message does not need to wait for the entry to be aged before updating, which can greatly reduce the time required for updating the entry. Usually, the link switching process can be completed within milliseconds, minimizing traffic loss.
Link Restoration Processing Principle
When the original active link recovers from failure, Interface1 will remain in the blocked state without preemption, thus keeping the traffic stable. If you want to switch traffic to the original active link, you can use the following two mechanisms to switch.
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To use the switchback function of the Smart Link group, the switchback function must be enabled on SwitchD. After the failure of the original active link recovers, Smart Link will automatically switch traffic to the original active link after the time set by the switchback timer.
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Use configuration commands to force the Smart Link to immediately switch traffic to the original active link.
As shown in the networking example shown in Figure 1, when the link of Interface1 on SwitchD recovers, if the Smart Link group switchback function is configured, after the switchback timer expires, Interface2 will be blocked and switch to the standby state, and Interface1 will switch to the standby state. Switch to forwarding state. However, if the configuration command is used to force the Smart Link to perform link switching, after the command is executed, Interface2 will be blocked immediately and switch to the standby state, while Interface1 will switch to the forwarding state.
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Purpose and advantages of Smart-Link
The downstream device is connected to the upstream device. When using the single uplink method, if a single point of failure occurs, the service will be interrupted. If the dual uplink method is used, one device is connected to two upstream devices at the same time, which can reduce the impact of single point failure on the network. impact, which improves reliability.
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As shown in Figure 1, SwitchA is connected to SwitchB and SwitchC respectively in dual uplink mode. In this way, there can be two links from SwitchA to SwitchD (SwitchA->SwitchB->SwitchD and SwitchA->SwitchC->SwitchD). The loop will generate a network storm. Configure Smart Link on SwitchA. Normally, the link where Interface2 resides can be used as a backup for the link where Interface1 resides. If the link where Interface1 is located fails, Smart Link will automatically switch the data traffic to the link where Interface2 is located to ensure uninterrupted services.
Using the Smart Link technology in this type of networking has the following advantages:
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It can be realized that when the two links of the dual uplink networking are normal, one link is in the forwarding state, while the other is in the blocking standby state, thereby avoiding the adverse effect of the loop.
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Configuration and use are more concise and user-friendly.
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When the primary link fails, the traffic will be quickly switched to the standby link within milliseconds, ensuring the normal forwarding of data to the greatest extent.
In the networking of some Layer 2 topology protocols (such as Smart Link), the topology protocol cannot monitor the status of the uplink interface, so the topology protocol cannot perform link switching. Monitor Link can be used to expand the application scope of some Layer 2 topology protocols. By monitoring the uplink and synchronously setting the downlink, the uplink fault can be quickly communicated to the downlink device, thereby triggering the topology protocol on the downstream device to perform link restoration. Switchover to prevent traffic loss due to uplink failure for a long time.
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Basic Smart-Link Load Balancing Configuration Example
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Configuration idea:
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Configure Switch1 to map VLAN 500 that needs to be load balanced to instance 10.
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Configure a Smart Link group on Switch1, and add the corresponding interfaces to the Smart Link group.
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Configure the load balancing function on Switch1, and forward the VLAN data mapped to instance 10 through the backup link.
Configure the load balancing function on Switch1
[Switch1-smlk-group1] load-balance instance 10 slave
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Enable the failback function on Switch1, so that after the fault is restored, the traffic is switched to the relatively stable original active link.
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Enable the function of sending Flush packets on Switch1.
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Enable the function of receiving Flush packets on the corresponding interfaces of Switch2, Switch3, and Switch4.
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Enable the Smart Link group function on Switch1.
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configuration command
SW1: # sysname SW1 # vlan batch 10 100 500 # stp region-configuration instance 10 vlan 500 active region-configuration # interface GigabitEthernet0/0/1 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable # interface GigabitEthernet0/0/2 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable # interface GigabitEthernet0/0/4 port link-type access port default vlan 500 # smart-link group 1 load-balance instance 10 slave restore enable smart-link enable port GigabitEthernet0/0/1 master port GigabitEthernet0/0/2 slave timer wtr 30 flush send control-vlan 10 password simple huawei123 # return SW2: # sysname SW2 # vlan batch 10 100 500 # interface GigabitEthernet0/0/1 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # interface GigabitEthernet0/0/2 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # return SW3： # sysname SW3 # vlan batch 10 100 500 # interface GigabitEthernet0/0/1 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # interface GigabitEthernet0/0/2 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # return SW4 # sysname SW4 # vlan batch 10 100 500 # interface GigabitEthernet0/0/1 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # interface GigabitEthernet0/0/2 port link-type trunk port trunk allow-pass vlan 10 100 500 stp disable smart-link flush receive control-vlan 10 password simple huawei123 # interface GigabitEthernet0/0/3 port link-type trunk port trunk allow-pass vlan 10 100 500 # return SW5 # sysname SW5 # vlan batch 10 100 500 # interface Vlanif1 ip address 192.168.1.254 255.255.255.0 # interface Vlanif500 ip address 192.168.5.254 255.255.255.0 # interface MEth0/0/1 # interface GigabitEthernet0/0/1 port link-type trunk port trunk allow-pass vlan 10 100 500 #
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Basic Concepts of Monitor Link
Basic Concepts of Monitor Link
Monitor Link performs synchronization settings on the downlink interface by monitoring the link where the uplink interface is located. Uplink interfaces and downlink interfaces that work together form a monitor link group.
Figure 1 Example of a monitor link network diagram
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Monitor Link group
A monitor link group is also called a monitor link group and consists of uplink interfaces and downlink interfaces. Members of a group can be a single interface, a static aggregation group, a manual aggregation group, or a Smart Link group. The Smart Link group can only be used as an uplink interface. The state of the downlink interface changes with the change of the uplink interface. As shown in Figure 1 , Interface1 and Interface2 form a Monitor Link group; Interface3 and Interface4 form a Monitor Link group.
Figure Example of Monitor Link networking diagram
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uplink interface
The uplink interface, also known as the Uplink interface, is the one to be monitored in the Monitor Link group. If the uplink interface fails, it means that the Monitor Link group fails, and the downlink interfaces of the group will be forcibly set to the Down state . As shown in Figure 1, Interface1 and Interface3 are uplink interfaces. The uplink can also be a Smart Link group. When the uplink is a Smart Link group, the uplink can be considered to be faulty only when both interfaces of the Smart Link group are in the Inactive state (including Down). As shown in Figure 2 , the Smart Link group serves as the uplink interface of the Monitor Link.
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Basic Principles of Monitor Link
Basic Principles of Monitor Link
Figure 1 Example of a monitor link network diagram
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After the Monitor Link group is configured, the uplink interface will be monitored in real time. Once the uplink interface fails, including link failure, OAM single-pass failure, or OAM connection failure, etc., all downlink interfaces of the group it belongs to will be forced to be Up. It is in ERROR-DOWN state. When the uplink returns to normal, restore the downlink interface.
As shown in Figure 1 , if the uplink where Interface1 is located fails, Monitor Link will force Interface2 to be in the ERROR-DOWN state. Therefore, SwitchC can detect that the link to SwitchA via SwitchB is faulty. When the uplink where Interface1 is located returns to normal, Monitor Link will cancel the ERROR-DOWN state that is mandatory for Interface2, and enable Interface2.
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When the uplink interface is in the Smart Link group, the uplink interface can be considered to be faulty only when both interfaces of the Smart Link group are in the Inactive state (including Down). When the downlink interface is an aggregation group, an uplink failure will force all interfaces in the aggregation group to be in the ERROR-DOWN state. Similarly, all interfaces in the aggregation group will be operated upon recovery.
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Comprehensive configuration of Smart-Link and Monitor Link
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Configure on the basis of Smart-link
SWB： # interface GigabitEthernet0/0/3 stp disable # smart-link group 1 port GigabitEthernet0/0/2 master port GigabitEthernet0/0/3 slave # monitor-link group 1 smart-link group 1 uplink port GigabitEthernet0/0/1 downlink 1 # return SWC： # monitor-link group 1 port GigabitEthernet0/0/2 uplink port GigabitEthernet0/0/1 downlink 1 # return[SwitchB]dis smart-link group 1 Smart Link group 1 information : Smart Link group was disabled There is no Load-Balance There is no protected-vlan reference-instance DeviceID: 4c1f-ccfb-254a Member Role State Flush Count Last-Flush-Time ---------------------------------------------------------------------- GigabitEthernet0/0/2 Master Unknown 0 0000/00/00 00:00:00 UTC+00 :00 GigabitEthernet0/0/3 Slave Unknown 0 0000/00/00 00:00:00 UTC+00 :00 [SwitchB]dis monitor-link group 1 Monitor Link group 1 information : Recover-timer is 3 sec. Member Role State Last-up-time Last-down-tim e Smart-link1 UpLk UP 0000/00/00 00:00:00 UTC+00:00 0000/0 0/00 00:00:00 UTC+00:00 GigabitEthernet0/0/1 DwLk[1] UP 2022/11/23 15:48:29 UTC-08:00 2022/1 1/23 15:45:39 UTC-08:00 [SwitchB]