4.4. Cables

Connecting cables between Gigabit NICs is very simple: The auto-negotiation feature between two NICs takes care about the crossover cable versus straight through cable detection and this section can be ignored.

Connecting cables toward Fast Ethernet NICs is pretty tricky: Everything towards a switch needs to be a straight through cable, everything else needs to be a crossover cable.

When a by-pass card gets turned off or disabled and the failure mode is fail-to-wire, it will act as a crossover cable.

4.4.1. Cabling for different scenarios

4.4.1.1. Single Steelhead appliance located between switch and router

The WAN router is connected via a crossover cable, the LAN switch is connected via a straight through cable.

During fail-to-wire a straight through cable is required.

Table 4.1. Cabling for placement of Steelhead appliance between switch and router

 InstallationFail to wire
WAN router to WAN interfacecrossover 
LAN switch to LAN interfacestraight through 
WAN router to LAN switch C + C + S -> straight through

4.4.1.2. Single Steelhead appliance located between two routers

The WAN router and the LAN router are connected via crossover cables to the Steelhead appliance.

During fail-to-wire a crossover cable is required.

Table 4.2. Cabling for placement of Steelhead appliance between two routers

 InstallationFail to wire
WAN router to WAN interfacecrossover 
LAN router to LAN interfacecrossover 
WAN router to LAN router C + C + C -> crossover cable

4.4.1.3. Serial Steelhead cluster located between switch and router

The WAN router is connected via a crossover cable, the two Steelhead appliances are connected via a crossover cable and the LAN switch is connected via a straight through cable.

During fail-to-wire a crossover cable is required for the Steelhead appliance to the WAN router, a straight through cable is required between the two Steelhead appliances and the LAN switch and a straight through cable is required between the WAN router and the LAN switch.

Table 4.3. Cabling for placement of two Steelhead appliances between switch and router

 InstallationFail to wire
WAN router to SH1 WAN interfacecrossover 
SH1 LAN interface to SH2 WAN interfacecrossover 
SH2 LAN interface to LAN switchstraight through 
WAN router to SH2 WAN interface C + C + C -> crossover
SH1 LAN interface to LAN switch C + C + S -> straight through
WAN router to LAN switch C + C + C + C + S -> straight through

4.4.1.4. Serial Steelhead cluster located between two routers

The WAN router and the LAN router are connected via crossover cables to the Steelhead-appliances, the two Steelhead appliances are connected via a crossover cable with each other.

During fail-to-wire crossover cables are required everywhere.

Table 4.4. Cabling for placement of two Steelhead appliances between two routers

 InstallationFail to wire
WAN router to SH1 WAN interfacecrossover 
SH1 LAN interface to SH2 WAN interfacecrossover 
SH2 LAN interface to LAN switchcrossover 
WAN router to SH2 WAN interface C + C + C -> crossover
SH1 LAN interface to LAN switch C + C + C -> crossover
WAN router to LAN switch C + C + C + C + C -> crossover

4.4.2. 100 Mbps fixed speed and MDI-X

When the Ethernet link is configured to 100 Mbps, it can happen that the Ethernet link doesn't come up because of a wrong cable type. Forcing the NIC to be MDI-X can resolve this:

Figure 4.3. Configuring interface wan0_0 with MDI-x

SH (config) # interface lan0_0 force-mdi-x enable
% Interface must be set to 100/full before enabling force mdi-x.
SH (config) # interface lan0_0 speed 100
SH (config) # interface lan0_0 duplex full
SH (config) # interface lan0_0 force-mdi-x enable
SH (config) # show interfaces force-mdi-x 
aux: false
inpath0_0: false
lan0_0: true
lo: false
primary: false
wan0_0: false

Afterwards, a check for the fail-to-wire scenario should be done when the Steelhead appliance is turned off.

4.4.3. Fiber by-pass card

When a Fiber by-pass card shows that it has detected an Ethernet link, it means that it has seen the light shone into the fiber string by the other side. So it is possible that the switch says it has detected a link, but that the Steelhead appliance says that it hasn't detected a link. The problem issue lies between the TX port of the switch and the RX port on the by-pass card.

4.4.4. VLAN bridge to overcome slow fixed speed LAN interfaces

When a fixed speed and duplex setting is used on the LAN and the WAN interface and the devices connected to them should all be at the same speed and duplex settings. If the WAN bandwidth is more than about ten percent of the fixed speed, it might be worth to implement a VLAN bridge to overcome the fixed speed requirement on the Steelhead appliance LAN/WAN interfaces.

For example if the WAN bandwidth is 5 Mbps and the WAN router is set to 10 Mbps, the speed of the optimized traffic coming out of the LAN interface is capped to 10 Mbps. Suddenly the LAN interface would be the limiting factor.

Also, the WAN router could be managed by a third party which means changing the interfaces to auto-negotiate is not possible. The way to overcome this is by creating a VLAN bridge on the LAN switch:

Figure 4.4. VLAN bridge to overcome fixed speed/duplex settings

VLAN bridge to overcome fixed speed/duplex settings

Port A should be set to the fixed speed and duplex setting of the WAN router. Port B and C should be set to auto-negotiation. The VLAN between port A and B should not have an IP address, it is just there to forward Ethernet packets.

This way, if the in-path interface goes into bypass, the LAN switch and WAN router are still able to talk to each other because the Ethernet link gets negotiated between port B and C.