Nexus 5020 10G long distance support

[Reece Boucher]

Greetings,

I have a configuration as per the attached diagram that has fibre distances of approx 20km.

Initially we configured a Layer 3 core between Data Centres using dark fibre and DWDM optics, and this has been working for several months.

To facilitate migrating workloads from DC1 to DC2 we used a different wavelength optic and did a Layer 2 'stretched' network to present the same VLANs in both DC1 and DC2.  This connection has been unstable and generally shows a 'Link not connected' message.

A TAC case was raised and they informed me there is no support for SFP-10G-ER on Nexus 5020, and that we need to upgrade our switch.

I can understand that viewpoint to an extent, however I am confused as to why the Layer 3 connection (using same optics different wavelength) works and is stable.

Anyone got any ideas?

[Walter Dey]

Hi Reece

Are you compliant with the SFP support matrix

http://www.cisco.com/c/en/us/td/docs/interfaces_modules/transceiver_modules/compatibility/matrix/10GE_Tx_Matrix.html#_Toc458157347

If the L2 link is not stable, you might see spanning tree running !

I can't see any other reason, why L3 should work, and L2 not ?

Is the distance within the power budget of the optics ? have there been recent fibre cuts and recovery ?

http://www.cisco.com/c/en/us/support/docs/optical-networking/ons-15454-sonet-multiservice-provisioning-platform-mspp/27042-max-att-27042.html

Table 2 – For Wavelength 1550nm

	Attenuation/ Km (dB/Km)	Attenuation/optical connector (dB)	Attenuation/joint (dB)
Min	0.17	0.2	0.01	Best Conditions
Average	0.22	0.35	0.05	Normal
Max	0.4	0.7	0.1	Worst situation

http://www.10gtek.com/templates/wzten/pdf/10GBASE-DenseSFP+.pdf

I believe 20km should not be a problem !

[Reece Boucher]

Walter,

Thanks for the reply.

No, we aren't compliant (and I accept that).What I'm curious about is why same optics (different wavelength) work but configuring the switchport as a Layer 2 trunk doesn't.

The distance is well within the power budget (40km), and no recent cuts (as stated, L3 is up and stable for months).  I have seen low Rx Power messages against the L2 connection but that in itself is surprising as it is sharing the same dark fibre as the L3 connection (unless there is an issue with the DWDM).

I have the L2 disconnected at the moment.  I'll see if there is a change when reconnected.

Reece.

[Walter Dey]

Hi Reece

Did ever switch the SFP from L2 to L3 and vice versa ?

Did you try to connect the links on 2 different interfaces ? (SFP ER might need to much current ?)