Cisco GLC-T Copper SFP Compatibility

Just a “gotcha”…. Before deciding to re-use GLC-T SFPs elsewhere in the network, be aware that the documentation states the following:

Speeds Supported by the 1000BASE-T(GLC-T) SFP Module on the Cisco Catalyst 3750 Series Switch
The 1000BASE-T SFP can support 10/100/1000 speeds only on the Cisco Catalyst 2970, 3560, and 3750 Series Switches.

Putting some these in other vendor’s (Juniper MX) kit and trying to use them caused a fair bit of confusion as we had all manner of problems getting them to work at 100 Mbit mode.

When set to auto where the other end was auto and only 100Mbit capable, sometimes the link light came up making us think it’d work fine but that wasn’t the case. We ended up ordering Juniper SFPs in the end and all the headaches went away.

Saving/Mailing Large “show tech” Output

Assuming you’re using a unix/linux management server, this is a quick and easy way to get a large “show tech” output to a file and mail it off elsewhere, assuming . If it’s leaving your organisation then you should either use 7zip or winzip or similar on your windows workstation to encrypt as the standard unix zip utility does not provide strong encryption.

me@mgmt-server# script lonsw02-tech.txt
Script started, file is lonsw02-tech.txt
me@mgmt-server# ssh lonsw02
LONSW02> en
LONSW02# term len 0
LONSW02# show tech-support
< output omitted >
LONSW02# exit
me@mgmt-server# ^D  ( CTRL + D )
Script done, file is lonsw02-tech.txt
me@mgmt-server# unix2dos lonsw02-tech.txt
unix2dos: converting file test.txt to DOS format ...
me@mgmt-server# uuencode lonsw02-tech.txt lonsw02-tech.txt | mailx -s "Show tech"

If your management server isn’t configured as a mail client, that can be fixed on RHEL with:

# vi /etc/sysconfig/sendmail


# vi /etc/mail/


Reload Sendmail

# service sendmail reload

Juniper BGP – “unsupported optional parameter” message

This seems to happen mainly with legacy kit such as old Nortel routers and the like. The peering won’t come up at all despite everything looking OK config wise.

When doing a bit more digging, the following message can be seen in the Juniper logs:

bgp_recv_open: peer x.x.x.x (External AS 12345): received NOTIFICATION code 2
 (Open Message Error) subcode 4 (unsupported optional parameter)

Solution (Example)

set protocols bgp group VENDORA neighbor disable-4byte-as

This sets the peering to 2 byte AS number support only and allows the peering to come up.

Migrating from Cisco to Juniper – Admin Distances

When migrating from Cisco to Juniper, care has to be taken because the two vendors have completely different values for default admin distances. If you haven’t come across this before then you’ll be scratching your head for a few minutes wondering why, for example, your traceroute is bouncing around your IGP and never heading out to eBGP.

A couple of examples:

Route Source Cisco Value Juniper Value
Connected interface 0 0
Static route 1 5
External Border Gateway Protocol (BGP) 20 170
OSPF 110 150
Intermediate System-to-Intermediate System (IS-IS) 115 160/165
Routing Information Protocol (RIP) 120 100
Internal BGP 200 170

BGP cost can be “fixed” globally to be Cisco equivalent if desired by the following example on Juniper:

set protocols bgp preference 20