03-17-2020 01:01 PM - edited 03-17-2020 01:03 PM
So I recently learned that Flex Links have been deprecated starting with early IOS-XE 16.x, but that there's a new feature called Flexlink+ that's available as of IOS-XE 16.12. When I found the config guide chapter for this feature, the config statements of interest are really REP statements. It's really a pretty short chapter with not a lot of explanation behind the Flexlink+ feature.
So what I'm wondering is:
Only asking these questions here as I can find next to no other information on Flexlink+.
Solved! Go to Solution.
03-18-2020 04:16 PM - edited 03-18-2020 04:28 PM
Hi!
REP is indeed a loop control protocol, primarily, but the configuration suggested uses only REP edge no-neighbor type of ports.
A REP edge no-neighbor port assumes whatever is connected to it is not a REP capable device. So, for practical purposes, it "disables" the loop control capabilities. REP also disables STP on the REP ports, and there is no configuration change required on the devices connected to it (they could be configured as STP portfast to enhance convergence times). This is usually done when you need to integrated a REP ring with an external network (STP).
Considering this, the Flexlink+ example uses a REP ring of a single switch, with this switch having both the Primary and Secondary edge ports, which in Flexlink terms will be the Active and backup ports, respectively.
The REP switch will have all VLANs allowed on Primary edge port, while the Secondary edge port will be in alternate/blocking state, for example:
AM270NP3102#show rep topology
REP Segment 1
BridgeName PortName Edge Role
-------------------------------- ---------- ---- ----
AM270NP3102 Gi1/13 Pri Open
AM270NP3102 Gi1/12 Sec Alt
If the Primary edge port fail, the Secondary edge port starts forwarding traffic. This achieves the same as Flexlink.
Convergence time for REP varies between platforms and depends on the size of the ring, but is said to be between 10 - 90 msecs. This being a REP ring of a single switch the convergence should be minimal as no exchange of REP LSL packets via the network happens.
VLAN load balancing is possible in REP too. Let's say you have VLANs 10 and 20. You want VLAN 10 to be forwarded out of the Primary edge port and VLAN 20 out of the Secondary edge port.
On the Primary edge-port, configure VLB to block VLAN 10 on the Secondary port with the following command:
Device(config)# interface x/x
Device(config-if)# switchport trunk allowed vlan 10,20
Device(config-if)# switchport mode trunk
Device(config-if)# rep segment 1023 edge no-neighbor primary
Device(config-if)# rep block port -1 vlan 10
This means, block VLAN 10 on the Secondary port (-1). Once this command is configured, the rest of VLANs not specified on the list will automatically be blocked on the Primary port (1). The result is only VLAN 10 is forwarding in Primary port, and only VLAN 20 is forwarding on Secondary port. A "show interface trunk" should show that.
VLB is not contemplated on the Flexlink+ document, and there is also no mention of the REP admin VLAN which is vital for VLB and preemption features. So will need to check if this is officially supported, but in good theory you should be able to load balance between REP ring ports even if it is just one switch.
Hope this helps.
03-18-2020 06:21 AM
I think the 9400 has other options for redundancy links
you can combine two uplink 9400's in a stackwise virtual configuration
for the connected switch both links can be member of a normal etherchannel
this way no need to for flex-link and/or spanning-tree
03-18-2020 07:16 AM
Maybe, but I wasn't asking about alternatives, I was asking specifically about the Flexlink+ feature in order to understand it better. No feature is perfect, there are always trade-offs :)
03-18-2020 08:25 AM - edited 03-18-2020 08:36 AM
ok no problem,
does this document help ?
Resilient Ethernet Protocol (REP) is a Cisco proprietary protocol that provides an alternative to the Spanning Tree Protocol (STP). REP provides fast reconvergence and traffic recovery when a link in a ring fails. Fast reconvergence is achieved by notifying all nodes in the ring with a control message that activates the redundant path to the core network.
and CiscoLive!
FLexlink+ may just be another name for REP?
Feature name |
Releases |
Feature Information |
---|---|---|
Flexlink+ |
Cisco IOS XE Gibraltar 16.12.1 |
The feature was introduced. |
03-18-2020 10:13 AM
Thanks, I have read that chapter, but that only raises more questions. Since REP is a loop topology protocol, I don't understand the applicability to Flex Links/Flexlink+, each of which are star topology things.
03-18-2020 04:16 PM - edited 03-18-2020 04:28 PM
Hi!
REP is indeed a loop control protocol, primarily, but the configuration suggested uses only REP edge no-neighbor type of ports.
A REP edge no-neighbor port assumes whatever is connected to it is not a REP capable device. So, for practical purposes, it "disables" the loop control capabilities. REP also disables STP on the REP ports, and there is no configuration change required on the devices connected to it (they could be configured as STP portfast to enhance convergence times). This is usually done when you need to integrated a REP ring with an external network (STP).
Considering this, the Flexlink+ example uses a REP ring of a single switch, with this switch having both the Primary and Secondary edge ports, which in Flexlink terms will be the Active and backup ports, respectively.
The REP switch will have all VLANs allowed on Primary edge port, while the Secondary edge port will be in alternate/blocking state, for example:
AM270NP3102#show rep topology
REP Segment 1
BridgeName PortName Edge Role
-------------------------------- ---------- ---- ----
AM270NP3102 Gi1/13 Pri Open
AM270NP3102 Gi1/12 Sec Alt
If the Primary edge port fail, the Secondary edge port starts forwarding traffic. This achieves the same as Flexlink.
Convergence time for REP varies between platforms and depends on the size of the ring, but is said to be between 10 - 90 msecs. This being a REP ring of a single switch the convergence should be minimal as no exchange of REP LSL packets via the network happens.
VLAN load balancing is possible in REP too. Let's say you have VLANs 10 and 20. You want VLAN 10 to be forwarded out of the Primary edge port and VLAN 20 out of the Secondary edge port.
On the Primary edge-port, configure VLB to block VLAN 10 on the Secondary port with the following command:
Device(config)# interface x/x
Device(config-if)# switchport trunk allowed vlan 10,20
Device(config-if)# switchport mode trunk
Device(config-if)# rep segment 1023 edge no-neighbor primary
Device(config-if)# rep block port -1 vlan 10
This means, block VLAN 10 on the Secondary port (-1). Once this command is configured, the rest of VLANs not specified on the list will automatically be blocked on the Primary port (1). The result is only VLAN 10 is forwarding in Primary port, and only VLAN 20 is forwarding on Secondary port. A "show interface trunk" should show that.
VLB is not contemplated on the Flexlink+ document, and there is also no mention of the REP admin VLAN which is vital for VLB and preemption features. So will need to check if this is officially supported, but in good theory you should be able to load balance between REP ring ports even if it is just one switch.
Hope this helps.
03-19-2020 01:07 AM
Flex Links
Flex Links are a pair of a Layer 2 interfaces (switch ports or port channels) where one interface is configured to act as a backup to the other. The feature provides an alternative solution to the Spanning Tree Protocol (STP). Users can disable STP and still retain basic link redundancy. Flex Links are typically configured in service provider or enterprise networks where customers do not want to run STP on the switch. If the switch is running STP, Flex Links is not necessary because STP already provides link-level redundancy or backup
=> from this text, flexlinks is not really a star-topology its just an interface pair
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide