Popular discussions about programming, compatibility and testing of optical transceivers.
Two Cisco Catalyst 3750-X switches (WS-C3750X-24P-L and WS-C3750X-48P-L) run identical code. A Cisco GLC-SX-MMD is detected normally in Gi1/1/1 of the first switch, but the second switch reports 'media type is Not Present' with 'link type is force-up' on Gi1/1/1, and 'show idprom interface Gi…
The poster asked why third-party SFP modules stopped working after upgrading Cisco switches to IOS 15.2, whereas other vendors accept Cisco or other optics, and whether this is a technical limitation. No model, log output or interface details were given despite requests. In a later update the…
The poster connected a Dell server to a Cisco Catalyst C9500-48Y4C (IOS XE 17.9.3) using a Dell L56SF018-SD-R 3 m DAC (DAC-SFP-3M). The cable is not in Cisco's optics compatibility matrix, and 'show interface status' shows port TwentyFiveGigE1/0/35 as err-disabled. Logging shows…
The poster's newly acquired Cisco Catalyst 9300 (with an 8-port 10G SFP+ network module) would not link to a Cisco Catalyst 4503-E that only has 1G SFP ports. Suspecting a 10G-versus-1G speed mismatch, the poster tried to force the 9300's 10G SFP to operate at 1G with the 'speed' command, but the…
A Cisco Nexus 5672UP fitted with a 10GBASE-SR SFP+ could not connect to another switch that uses a 1000BASE-SX (1 Gbps) transceiver; both ends are multimode optics. When the poster changed the port speed, 'show interface brief' displayed an 'SFP checksum error', and swapping the Nexus optic for a 1…
The poster needs a 100GE link between a Cisco NCS55A2-MOD (NC55-MPA-4H-S MPA) and a Cisco Catalyst C9500-48Y4C using a QSFP-100G-CU1M DAC. Both platforms list the cable as supported, yet the link never comes up at the physical level. Because the Catalyst 9500 lacks 100G auto-negotiation (bug…
The poster uses Ubiquiti (UBNT) SFP and SFP+ modules, both multimode and single-mode, in Cisco switches. They work perfectly in Catalyst 9300 and 3650 switches with current IOS, but in a Catalyst C1000 and a Catalyst 2960 the modules are detected on insertion yet reported as 'unknown' in 'show…
The poster wanted to run 100 Mbps fibre SFP modules in a D-Link DES-3200-28F but the vendor compatibility list only named older switches (DES-1228, DES-1252, DGS-3612G). The question was whether the list was simply stale or whether the modules would be rejected by the newer switch. A related…
The poster (in a machine-translated post from the Spanish-language community) tried to connect two Cisco Business CBS350-24T-4X switches through their SFP+ ports using MikroTik XS+2733LC15D modules. No connectivity is established and the ports end up blocked by the switch's Link Flap Prevention…
Two Cisco Catalyst C1200-48T-4X switches were connected back-to-back with Cisco SFP-10G-LR modules in the ge49/te1 SFP+ slots. Both switches recognize the transceivers, the interfaces are administratively up, both ends transmit light and the DOM optical values are good, yet no link is established…
The poster owned a MikroTik RB962UiGS-5HacT2HnT (hAP ac) with a single SFP cage and had two spare 850 nm modules on hand: a Cisco-branded AFBR-57F5PZ-CS1 and an Intel-branded FTLX8571D3BCVIT1. The ISP delivered the service over a single fibre strand rather than a duplex pair, and the poster wanted…
Juniper-branded SFP modules were intermittently reported as unsupported or not supported in the chassis hardware output right after an EX or MX device booted. Rebooting the device or reseating the SFP made the module recognised again, which was frustrating in production. The poster wanted to know…
Before replacing an old switch with a Cisco Catalyst 9300-M, the poster wanted to know whether the existing SFP could be reused and posted the 'show idprom interface gigabitEthernet 1/1/1' output: Vendor Name CISCO-FINISAR, Vendor Part Number FTLF1318P2BCL-C3, serial FNS15510U5B, 1310 nm, single…
In the poster's data center several Cisco CWDM SFP/GBIC links stopped working: some ports went err-disabled (one with link-flap as the cause) and others simply showed notconnect. Troubleshooting included shut/no shut, reseating the modules, moving the CWDM SFPs to other ports, replacing the patch…
Two Cisco Nexus 93108TC-FX3P switches on NX-OS 9.3(11) are connected with genuine QSFP-100G-CU1M DACs but the link never comes up. The compatibility matrix says the cable is supported from NX-OS 9.3.5. The port config is a plain 'switchport mode trunk' / 'no shutdown', and 'show interface eth1/54…