<div>
<div class="content wysiwyg-content">
there is a link between backbone sw and access sw on the access part the interfaces always go down cause of udld error disable although the backbone sw connected to 10 swi all have the same configuration but this problem appears only on one sw of them <br />

<pre><code id="code-234286">BB1
!
int gi 1/19
switchport trunk encapsulation dot1q
switchport mode trunk 
switchport trunk native vlan 37
switchport trunk allwed vlan 37
udld port
! 
Access Sw
!
int gi 0/1
switchport mode trunk 
switchport trunk native vlan 37
switchport trunk allwed vlan 37
!
</code></pre>
</div>
</div>


there is a link between backbone sw and access sw on the access part the interfaces always go down cause of udld error disable although the backbone sw connected to 10 swi all have the same configuration but this problem appears only on one sw of them 

what causes the udld error disable

A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.