Why is there still a physical link when performing ifdown eth0?

Issue

• One of our server running RHEL 6.2 or RHEL 5. The available Ethernet port (eth0) is driven by the Intel igb driver. When the port is turned off (ifconfig down), the link status at the other end (an Ethernet switch) remains up.

• Port is administratively down (flags up & running are not active)

$ ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:11:3F:CD:5E:27
          inet addr:192.168.0.4  Bcast:192.168.0.255  Mask:255.255.255.0
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:40259 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7560 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:5959823 (5.6 MiB)  TX bytes:1098413 (1.0 MiB)
          Memory:fbc80000-fbd00000

$ ethtool eth0
Settings for eth0:
         Supported ports: [ TP ]
         Supported link modes:   10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Supports auto-negotiation: Yes
         Advertised link modes:  10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Advertised pause frame use: No
         Advertised auto-negotiation: Yes
         Speed: 1000Mb/s
         Duplex: Full
         Port: Twisted Pair
         PHYAD: 1
         Transceiver: internal
         Auto-negotiation: on
         MDI-X: Unknown
         Supports Wake-on: pumbg
         Wake-on: d
         Current message level: 0x00000003 (3)
         Link detected: yes

• From the switch perspective, the the port is still up (operational statue)

       ena/  speed/  link  auto    STP                   lrn  inter max  loop
port  link  duplex  scan  neg?   state   pause  discrd  ops   face frame  back
ge19  up     1G FD    SW   Yes  Forward  TX RX   None    FA  SGMII 1518

• When the interface has been shutdown, it is no longer functional for ping, telnet, ssh etc.