MDI-X Autonegociacion

Hay gente que le gusta forzar los parámetros speed y duplex en las interfaces por que no se fia de la autonegociación, bien, pero en todos los casos no es correcto.
¿Cuando no es correcto? cuando entre dos switches nos conectan un cable no-cruzado.


Y ¿como sabemos si el cable no es cruzado? Para un switch 3560

show interface (no sirve)
show ip interface (no sirve)
show switchport (no sirve)
show switchport capabilities (no sirve)
El único comando que sirve es
show controllers ethernet fa0/1 phy

Pongo un ejemplo
3750#sh controllers ethernet-controller gig1/0/18 phy

GigabitEthernet1/0/18 (gpn: 18, port-number: 18)
-----------------------------------------------------------
 0000: 1140 Control Register                      :  0001 0001 0100 0000
 0001: 796D Control STATUS                        :  0111 1001 0110 1101
 0002: 0020 Phy ID 1                              :  0000 0000 0010 0000
 0003: 63B0 Phy ID 2                              :  0110 0011 1011 0000
 0004: 01E1 Auto-Negotiation Advertisement        :  0000 0001 1110 0001
 0005: 4181 Auto-Negotiation Link Partner         :  0100 0001 1000 0001
 0006: 0005 Auto-Negotiation Expansion            :  0000 0000 0000 0101
 0007: 2001 Next Page Transmit                    :  0010 0000 0000 0001
 0008: 0000 Next Page Receive                     :  0000 0000 0000 0000
 0009: 0600 1000BaseT Control                     :  0000 0110 0000 0000
 000A: 0000 1000Base-T Status                     :  0000 0000 0000 0000
 000F: 3000 IEEE Extended Status                  :  0011 0000 0000 0000
 0010: 0001 Phy Extended Control                  :  0000 0000 0000 0001
 0011: 0300 Phy Extended Status                   :  0000 0011 0000 0000
 0012: 0000 Receive Error Counter                 :  0000 0000 0000 0000
 0013: 0000 False Carrier Sense Counter           :  0000 0000 0000 0000
 0014: 0000 Receiver NOT_OK Counter               :  0000 0000 0000 0000
 0019: 8514 Auxiliary Status Summary              :  1000 0101 0001 0100
 001A: 0000 Interrupt Status                      :  0000 0000 0000 0000
 001B: FFFF Interrupt Mask                        :  1111 1111 1111 1111
 001C: 7CFC Control Reg 2                         :  0111 1100 1111 1100
 001D: 056E Spare Control Register                :  0000 0101 0110 1110
 001E: 0000 Test Register 1                       :  0000 0000 0000 0000
 Auto-MDIX                             :  On   [AdminState=1   Flags=0x00052248]


Shadow Registers
-----------------
 0018: 4400 Auxiliary Control                     :  0100 0100 0000 0000
 0018: 0001 10-BaseT Register                     :  0000 0000 0000 0001
 0018: 0502 Power/MII Control                     :  0000 0101 0000 0010
 0018: 0004 Miscellaneous Test                    :  0000 0000 0000 0100
 0018: 7077 Miscellaneous Control                 :  0111 0000 0111 0111
 001C: 0800 Spare Control 1                       :  0000 1000 0000 0000
 001C: 0C00 Clock Alignment Control               :  0000 1100 0000 0000
 001C: 100C Spare Control 2                       :  0001 0000 0000 1100
 001C: 141E Spare Control 3                       :  0001 0100 0001 1110
 001C: 214E LED Status Register                   :  0010 0001 0100 1110
 001C: 2408 LED Control Register                  :  0010 0100 0000 1000
 001C: 2801 Auto Power-Down                       :  0010 1000 0000 0001
 001C: 2C00 External Control 1                    :  0010 1100 0000 0000
 001C: 34EE LED Selector 1                        :  0011 0100 1110 1110
 001C: 386E LED Selector 2                        :  0011 1000 0110 1110
 001C: 3CF0 LED GPIO Control Status               :  0011 1100 1111 0000
 001C: 5C00 Misc 1000-X Control                   :  0101 1100 0000 0000
 001C: 6004 Autodetect SGMII/Media Convert        :  0110 0000 0000 0100
 001C: 68C0 Auto-Negotiation Debug                :  0110 1000 1100 0000
 001C: 6C87 Aux 1000Base-X Control                :  0110 1100 1000 0111
 001C: 700C Aux 1000Base-X Status                 :  0111 0000 0000 1100
 001C: 7400 Misc 1000Base-X Status                :  0111 0100 0000 0000
 001C: 7822 Auotodetect Medium                    :  0111 1000 0010 0010
 001C: 7CFC Mode Control                          :  0111 1100 1111 1100
00-10-18, 3B-00, 01-02

Si necesita negociación y el puerto esta forzado tanto por speed o por duplex el puerto aparecerá down down haciéndonos pensar que hay un problema en el enlace.

1 comentario:

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