Cisco Catalyst 2950, ​​traffic in one Vlan?

Question

Cisco

Good afternoon. I study cisco routers.
There is a catalyst 2950, ​​there are several "specialized" devices with ethernet ports. These modems, let's call them that, use a variety of protocols, they also use broadcast.
I created several vlans to separate the new subnets. In the default #1 I use the local LAN, the rest I use vlan #2 #3 for these modems.
But the trouble is that the traffic you need does not go, as far as I understand, from port to port in one vlan.
Moreover, if these modems are connected not through separate vlan ciscos, but through 8 port switches, then everything works fine.
What am I doing wrong?
Vlan

Switch#sh vl<br/>
<br/>
VLAN Name Status Ports<br/>
---- -------------------------------- --------- -------------------------------<br/>
1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5<br/>
 Fa0/6, Fa0/7, Fa0/8, Fa0/15<br/>
 Fa0/16, Fa0/17, Fa0/18, Fa0/19<br/>
 Fa0/20, Fa0/21, Fa0/22, Fa0/23<br/>
 Fa0/24<br/>
2 cisco_vlan_2 active Fa0/9, Fa0/10, Fa0/11<br/>
3 cisco_vlan_3 active Fa0/12, Fa0/13, Fa0/14<br/>
1002 fddi-default act/unsup<br/>
1003 token-ring-default act/unsup<br/>
1004 fddinet-default act/unsup<br/>
1005 trnet-default act/unsup<br/>
<br/>
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2<br/>
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------<br/>
1 enet 100001 1500 - - - - - 0 0<br/>
2 enet 100002 1500 - - - - - 0 0<br/>
3 enet 100003 1500 - - - - - 0 0<br/>
1002 fddi 101002 1500 - - - - - 0 0<br/>
1003 tr 101003 1500 - - - - - 0 0<br/>
1004 fdnet 101004 1500 - - - ieee - 0 0<br/>
<br/>
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2<br/>
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------<br/>
1005 trnet 101005 1500 - - - ibm - 0 0<br/>
<br/>
Remote SPAN VLANs<br/>
------------------------------------------------------------------------------<br/>
<br/>
Primary Secondary Type Ports<br/>
------- --------- ----------------- ------------------------------------------<br/>
<br/>
Switch#

Switch config:

Switch#sh ru<br/>
Building configuration...<br/>
<br/>
Current configuration : 1711 bytes<br/>
!<br/>
version 12.1<br/>
no service pad<br/>
service timestamps debug uptime<br/>
service timestamps log uptime<br/>
no service password-encryption<br/>
!<br/>
hostname Switch<br/>
!<br/>
!<br/>
ip subnet-zero<br/>
!<br/>
!<br/>
spanning-tree mode pvst<br/>
no spanning-tree optimize bpdu transmission<br/>
spanning-tree extend system-id<br/>
!<br/>
!<br/>
!<br/>
!<br/>
interface FastEthernet0/1<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/2<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/3<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/4<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/5<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/6<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/7<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/8<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/9<br/>
 switchport access vlan 2<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/10<br/>
 switchport access vlan 2<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/11<br/>
 switchport access vlan 2<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/12<br/>
 switchport access vlan 3<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/13<br/>
 switchport access vlan 3<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/14<br/>
 switchport access vlan 3<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/15<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/16<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/17<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/18<br/>
 spanning-tree portfast<br/>
!<br/>
interface FastEthernet0/19<br/>
!<br/>
interface FastEthernet0/20<br/>
!<br/>
interface FastEthernet0/21<br/>
!<br/>
interface FastEthernet0/22<br/>
!<br/>
interface FastEthernet0/23<br/>
!<br/>
interface FastEthernet0/24<br/>
!<br/>
interface Vlan1<br/>
 no ip address<br/>
 no ip route-cache<br/>
 shutdown<br/>
!<br/>
interface Vlan2<br/>
 no ip address<br/>
 no ip route-cache<br/>
!<br/>
ip http server<br/>
!<br/>
line con 0<br/>
line vty 5 15<br/>
!<br/>
!<br/>
end<br/>
<br/>
Switch#

Answer 1

Perhaps the modems are using a non-standard MTU (>1500). Jumbo Frames may be automatically enabled on a "stupid" switch, try enabling it on Cisco as well.

Answer 2

for completeness
sh int stats
sh int status
sh span blockedports
sh mac-add

Answer 3

vlans are native everywhere?

Answer 4

Based on the output of sh run, I propose to do
the following: - firstly, add vlan 3 to the vlan database - it is not defined for you at all. This must be done.
- secondly, the tsiska strongly recommends saying the “switchport mode access” command if you nail the port to the vlan.

Answer 5

Tell me, in which ports do you have these modems sticking out? And how do you check their performance?