I had the weirdest of a problem. Two computers communicating with each other over ping and TFTP works. When I boot one of them into U-boot (a bootloader that supports TFTP boot) it can’t ping not load tftp of the other machine complaining on ARP timeouts.

I swapped with a dumb switch - all works. Everything else (machines, cables) are the same. The managed switch is a Cisco switch and I have a serial console to it, but I’m not familiar with managing those switches - what feature is potentially blocking u-boot’s arp packets?

I’ve double checked with tcpdump - the other machine never seer u-boot’s arp packets, but does when the same board is booted into Linux. I’ve also checked Cisco’s monitor event-trace arp continuous and it didn’t print any packets but it did say link status went from up to down to back up when I rebooted.

Here’s the switch config - I removed exclamation marks because there isn’t much. The u-boot board is on port 1/0/6, the TFPT server is on 1/0/1

version 15.0
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname switch
boot-start-marker
boot-end-marker
no aaa new-model
switch 1 provision ws-c2960s-48td-l
spanning-tree mode pvst
spanning-tree extend system-id
vlan internal allocation policy ascending
interface FastEthernet0
 no ip address
interface GigabitEthernet1/0/1
interface GigabitEthernet1/0/2
interface GigabitEthernet1/0/3
interface GigabitEthernet1/0/4
interface GigabitEthernet1/0/5
interface GigabitEthernet1/0/6
interface GigabitEthernet1/0/7
interface GigabitEthernet1/0/8
interface GigabitEthernet1/0/9
interface GigabitEthernet1/0/10
interface GigabitEthernet1/0/11
interface GigabitEthernet1/0/12
interface GigabitEthernet1/0/13
interface GigabitEthernet1/0/14
interface GigabitEthernet1/0/15
interface GigabitEthernet1/0/16
interface GigabitEthernet1/0/17
interface GigabitEthernet1/0/18
interface GigabitEthernet1/0/19
interface GigabitEthernet1/0/20
interface GigabitEthernet1/0/21
interface GigabitEthernet1/0/22
interface GigabitEthernet1/0/23
interface GigabitEthernet1/0/24
interface GigabitEthernet1/0/25
interface GigabitEthernet1/0/26
interface GigabitEthernet1/0/27
interface GigabitEthernet1/0/28
interface GigabitEthernet1/0/29
interface GigabitEthernet1/0/30
interface GigabitEthernet1/0/31
interface GigabitEthernet1/0/32
interface GigabitEthernet1/0/33
 switchport access vlan 103
 switchport mode access
interface GigabitEthernet1/0/34
 switchport access vlan 103
 switchport mode access
interface GigabitEthernet1/0/35
 switchport access vlan 103
 switchport mode access
interface GigabitEthernet1/0/36
 switchport access vlan 103
 switchport mode access
interface GigabitEthernet1/0/37
 switchport access vlan 102
 switchport mode access
interface GigabitEthernet1/0/38
 switchport access vlan 102
 switchport mode access
interface GigabitEthernet1/0/39
 switchport access vlan 102
 switchport mode access
interface GigabitEthernet1/0/40
 switchport access vlan 102
 switchport mode access
interface GigabitEthernet1/0/41
 switchport access vlan 101
 switchport mode access
interface GigabitEthernet1/0/42
 switchport access vlan 101
 switchport mode access
interface GigabitEthernet1/0/43
 switchport access vlan 101
 switchport mode access
interface GigabitEthernet1/0/44
 switchport access vlan 101
 switchport mode access
interface GigabitEthernet1/0/45
 switchport access vlan 100
 switchport mode access
interface GigabitEthernet1/0/46
 switchport access vlan 100
 switchport mode access
interface GigabitEthernet1/0/47
 switchport access vlan 100
 switchport mode access
interface GigabitEthernet1/0/48
 switchport access vlan 100
 switchport mode access
interface GigabitEthernet1/0/49
interface GigabitEthernet1/0/50
interface TenGigabitEthernet1/0/1
interface TenGigabitEthernet1/0/2
interface Vlan1
 no ip address
ip http server
ip http secure-server
line con 0
line vty 5 15
end