28 Apr

How to Run 40GbE Over Duplex LC MMF Cabling

This is a good guide for running 40G on existing MMF fiber.

The use of parallel optics in 40GbE multimode fiber cabling (MMF cabling) require more fiber strands than the 10GbE infrastructures. Thus, data center will require a cabling upgrade to meet the requirement of migration. In this case, cost is a big factor. To help user solve the fiber cost issue, many vendors developed a new transceiver alternative that allow zero-cost fiber migration by reusing the current 10Gbps multimode fiber-optic cabling plant for 40Gbps connectivity. This post will introduce three mainstream transceiver options for running 40GbE over duplex multimode fiber cable with LC connectors.Option 1: Cisco QSFP 40G BiDi Transceiver (QSFP-40G-SR-BD)

The Cisco QSFP BiDi transceiver can transmit full-duplex 40Gbps traffic over one duplex OM3 or OM4 MMF cable with LC connector. It provides the capability to reuse 10Gbps fiber infrastructure, enabling data center operators to upgrade to 40Gbps connectivity without making any changes to the previous 10GbE infrastructures.

The working principle of Cisco QSFP BiDi transceiver is that it uses two 20Gbps channels, each transmitted and received simultaneously over two wavelengths on a single MMF strand, as shown in the following.


Concept of QSFP BiDi transceiver

Cisco QSFP BiDi transceiver can be supported in most Cisco switching and routing products that support 40GbE interfaces. The connection distance can reach up to 100 meters over OM3 MMF or 150 meters over OM4 MMF, which is the same as 40GBASE-SR4 QSFP+.

Note: The other version of Cisco QSFP BiDi transceiver (QSFP-40G-BD-RX) is almost the same with the QSFP-40G-SR-BD, but with link monitor hardware, such as the Cisco Nexus® Data Broker.

Option 2: Juniper 40Gbps QSFP+ LX4 (JNP-QSFP-40G-LX4)

Juniper 40Gbps QSFP+ LX4 module uses the same infrastructure as 10GbE. The LX4 technology represents a new way to deploy 40GbE that meets all of the performance criteria of today’s data centers by providing 40GbE on two MMF strands with duplex LC connectors. Thus, users can simply replace existing 10GbE transceiver modules with 40GbE LX4 modules without expensive 40GbE migration cassettes and additional fiber infrastructure.

As the following picture shown, QSFP+ LX4 transceiver uses four 10Gbps channels, each transmitted and received simultaneously over four wavelengths on a single MMF strand. Similar with the 40GBASE-SR4 modules, it can also support transmission distance up to 100 meters over OM3 MMF or 150 meters over OM4 MMF cable. Juniper 40Gbps QSFP+ LX4 can be supported in many Juniper devices that support 40GbE interface, such as QFX3000 QFabric system, QFX5100 switches, and so on.


Concept of QSFP+ LX4 transceiver

Note: The Juniper 40Gbps QSFP+ LX4 also support to run over single-mode fiber (SMF: OS1) and reach up to 2 kilometers.

Option 3: Arista Networks QSFP-40G-UNIV Transceiver

The Arista networks QSFP-40G-UNIV is a 40GbE QSFP+ transceiver with a duplex LC connector that can be used with both MMF and SMF. Its working principle is similar with the Juniper LX4 mentioned above, having 4 channels of 10G multiplexed inside the module to transmit and receive an aggregate 40Gbps signal over 2 strands of fiber. UNIV is short for the word “universal” because of its ability to operate with both MMF and SMF without the need for any software/hardware changes to the module or any additional hardware in the network. The Arista networks QSFP-40G-UNIV can operates on OM3 or OM4 MMF for distance up to 100 meters or SMF (OS1) for distance up to 500 meters. It is noted that this QSFP module can interoperate with Cisco and other vendors standards based 40GbE LR4 optics.

Credit: http://www.fiber-optic-transceiver-module.com/how-to-run-40gbe-over-duplex-lc-mmf-cabling.html

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19 Mar

Default routes in BGP

There are 3 ways of advertising default route in BGP.

Method 1: Using network command.
It requires only that the route is present in the Interior Gateway Protocol (IGP) routing table. This is the preferred approach.

Method 2: Using default-information originate command.
It requires explicit redistribution of the route This protects against someone accidentally redistributing a default route in BGP which could potentially be disastrous.

Method 3: Using neighbor default-originate command.
This method does not require the presence of the network in the routing table of the advertising router.



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13 Feb

Arista EOS 101

This is a simple short notes taken from Arista Configuration Essentials (ACE) Lab Guide


Enter bash
switch# bash
switch-bash$ ifconfig -a
switch-bash$ top
switch-bash$ cd /mnt/flash

Upgrade EOS

Upload EOS to switch
switch# copy flash:

Verify image
switch# dir flash:

Configure boot image
switch# boot system flash: EOS-4.15.5M.swi

Verify boot-config
switch# show boot-config


Configure port channel for your peerlink
switch# interface Ethernet47-48
switch# channel-group 1000 mode active
switch# interface port-channel 1000
switch# switchport mode trunk

Configure a VLAN and trunk group used for MLAG peer communications
switch# vlan 9094
switch# trunk group mlagpeer

Assign the port-channel to the trunk group
switch# interface po1000
switch# switchport trunk group mlagpeer

Disable STP on the VLAN used for the MLAG peer
switch# no spanning-tree vlan 4094

Configure SVI for peer-to-peer communications
switch# int vlan 4094
switch# ip address
switch# no autostate

Configure local interface and peer address
switch# mlag configuration
switch# local-interface vlan 4094
switch# peer-address

Configure domain-d, peer-link & reload-delay on BOTH switches
switch# domain-id mlagDomain
switch# peer-link port-channel 1000
switch# reload-delay 200

Configure the MLAG interface (upstream interface to spine)
switch# int Eth31-32
switch# channel-group 999 mode active
switch# int po999
switch# mlag 999

Optional (configure Virtual ARP for downstream device)
switch# ip virtual-router address 001c.7300.0009 (for both switches)
switch# int vlan 2 (for both switches)
switch# ip address
switch# ip virtual-router address (for both switches)

Verify MLAG
switch# show mlag
switch# show mlag config-sanity
switch# show mlag detail
switch# show mlag interfaces
switch# show int po999


switch-XX# interface Vxlan 1
switch-XX# vxlan source-interface Loopback 1
switch-XX# vxlan vlan 101 flood vtep
switch-XX# vxlan udp-port 4789
switch-XX# vxlan vlan 101 vni 10000

switch-YY# interface Vxlan 1
switch-YY# vxlan source-interface Loopback 1
switch-YY# vxlan vlan 101 flood vtep
switch-YY# vxlan udp-port 4789
switch-YY# vxlan vlan 101 vni 10000

Verify vxlan
switch# sh vxlan vtep
switch# sh vxlan address-table


Configure port mirror to CPU (control plane)
switch# monitor session sniff source Eth33 both
switch# monitor session sniff destination Cpu

switch# bash
switch-bash$ tcpdump -i mirror1

*use the mirror number from “sh monitor session” output (Cpu : active (mirror1)

BGP Path Selection

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11 Feb


RIB – Routing Information Base
FIB – Forwarding Information Base

This is a routing protocols database of routing prefixes that could potentially be installed in the routing table.
Derived from the control plane, it is not used for forwarding.
Every protocol such as OSPF, EIGRP, BGP has its own RIB and select their best candidates to try to install to global RIB so that it can then be selected for forwarding.
Is a selection of routing information learned via static definition or a dynamic routing protocol.
EX: show ip ospf databse show ip eigrp topology show ip bgp etc

The actual information that a routing/switching device uses to choose the interface that a given packet will use for egress.
Used for forwarding, information is derived from the RIB and from adjacency tables so that the packet can be rewritten with the correct encapsulation.
Is programmed by one or more RIB.
EX: show ip cef

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18 Jan

BGP RIB-Failure

When a Router receives a BGP UPDATE packet that contains Network Layer Reachability Information (NLRI) – this is, a route; the packet is processed in the next order:

– Step 1. BGP checks for the NLRI (prefix received) against any BGP inbound filter configured on the Router.

– Step 2. If the NLRI is not filtered, the prefix can be seen in the BGP table with the show ip bgp command.

– Step 3. If the Routing Table already has the same prefix/prefix-length entry with a lower Administrative Distance (AD) as seen in show ip route, BGP marks the route received with RIB-Failure.

*You can display BGP routes that are not inserted in the IP routing table with the show ip bgp rib-failure command, which also explains why the BGP route was not inserted in the IP routing table.

*all routes shown in show ip bgp rib-failure command will still advertised to all BGP peers.

*Network Layer Reachability Information (NLRI)

The Network Layer Reachability Information (NLRI) is exchanged between BGP routers using UPDATE messages. An NLRI is composed of a LENGTH and a PREFIX. The length is a network mask in CIDR notation (eg. /25) specifying the number of network bits, and the prefix is the Network address for that subnet.

The NLRI is unique to BGP version 4 and allows BGP to carry supernetting information, as well as perform aggregation.

The NLRI would look something like one of these:

     /23, 206.134.32
     /8, 10

1. https://blog.ipspace.net/2007/12/what-is-bgp-rib-failure.html
2. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/213286-understand-bgp-rib-failure-and-the-bgp-s.html#anc4
3. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5816-bgpfaq-5816.html#anc27