{"id":585,"date":"2021-01-18T08:28:20","date_gmt":"2021-01-18T14:28:20","guid":{"rendered":"http:\/\/jmcristobal.com.mx\/?p=585"},"modified":"2022-02-12T10:21:53","modified_gmt":"2022-02-12T18:21:53","slug":"udld","status":"publish","type":"post","link":"http:\/\/ec2-52-7-70-250.compute-1.amazonaws.com\/es\/2021\/01\/18\/udld\/","title":{"rendered":"UDLD &#8211; UniDirectional Link Detection"},"content":{"rendered":"<p lang=\"es-MX\">UDLD  es un protocolo de capa 2 propietario de Cisco que monitorea el estado de un puerto para validar la comunicaci\u00f3n bidireccional.<\/p>\n<p lang=\"es-MX\">Recordemos que cada puerto en un swtich es bidireccional, cuantan con un transmisor (Tx) y  un receptor (Rx) para intercambiar los  bits.<\/p>\n<p lang=\"es-MX\">El switch env\u00eda un frame especial a la direccion mac destino 01-00-0C-CC-CC-CC que identifica el dispositivo y id del puerto, el switch local espera recibir una contestaci\u00f3n desde el equipo remoto con la informaci\u00f3n similar del switch remoto, si el switch recibe esta respuesta considera que el enlace es bidireccional, de caso contrario se considera unidireccional<\/p>\n<p lang=\"es-MX\">Los mensajes UDLD se env\u00edan cada 15 segundos por default. UDLD puede detectar un enlace unidireccional despu\u00e9s de aproximadamente tres veces el intervalo de tiempo en que se env\u00eda los mensajes UDLD (45 segundos en total, utilizando el valor predeterminado)<\/p>\n<p lang=\"es-MX\">UDLD tiene dos modos de operaci\u00f3n:<\/p>\n<ul type=\"disc\">\n<li><span lang=\"es-MX\">Normal<\/span><span lang=\"x-none\">cuando se detecta una condici\u00f3n de enlace unidireccional, el puerto puede continuar su operaci\u00f3n. UDLD simplemente marca el puerto como que tiene un estado indeterminado y genera un mensaje syslog.<\/span><\/li>\n<li><span lang=\"es-MX\">Aggressive<\/span><span lang=\"x-none\">: cuando se detecta una condici\u00f3n de enlace unidireccional, el switch toma medidas para restablecer el enlace. Los mensajes UDLD se env\u00edan una vez por segundo durante 8 segundos. Si ninguno de esos mensajes se repite, el puerto se coloca en el estado errdisable para que no se pueda usar.<\/span><\/li>\n<\/ul>\n<p lang=\"es-MX\">UDLD est\u00e1 deshabilitado por default y para que funcione debe de estar configurado en ambos equipos.<\/p>\n<p lang=\"es-MX\">Se puede configurar UDLD por puerto, aunque puede habilitarlo globalmente para todos los puertos de fibra \u00f3ptica del switch<\/p>\n<p lang=\"es-MX\">Habilitarlo globalmente (solo aplica para puertos de fibra)<\/p>\n<pre class=\"height-set:true height:700 width-set:true width:700 top-margin:25 left-set:true left-margin:25 toolbar:2 lang:sh decode:true\">Switch(config)# udld { enable | aggressive | message time seconds}<\/pre>\n<ul>\n<li>Enable = Modo de operaci\u00f3n normal<\/li>\n<li>Aggressive = Modo de operaci\u00f3n agresivo<\/li>\n<\/ul>\n<p>Habilitar o deshabilitar UDLD en cada interfaz<\/p>\n<pre class=\"height-set:true height:700 width-set:true width:700 top-margin:25 left-set:true left-margin:25 toolbar:2 lang:sh decode:true\">Switch(config-if)# udld { enable | aggressive | disable}<\/pre>\n<p>Comando de verificaci\u00f3n:<\/p>\n<pre class=\"height-set:true height:700 width-set:true width:700 top-margin:25 left-set:true left-margin:25 toolbar:2 lang:sh decode:true\">!\n# show udld g0\/1\n!<\/pre>\n<p lang=\"es-MX\">Los medios de cobre  no sufren las condiciones de capa f\u00edsica que permiten la formaci\u00f3n de un enlace unidireccional. Sin embargo, puede habilitar UDLD en enlaces que no sean de fibra individualmente, si lo desea.<\/p>\n<p lang=\"es-MX\">Al configurar por primera vez UDLD no tiene registro de ning\u00fan vecino en el enlace. Si el switch vecino a\u00fan no tiene UDLD habilitado, no se reproducir\u00e1n los mensajes. UDLD seguir\u00e1 intentando (indefinidamente) detectar un vecino y no deshabilitar\u00e1 el enlace.<\/p>\n<p lang=\"es-MX\">Una vez que el vecino tiene UDLD configurado tambi\u00e9n, ambos switches se conocen uno al otro . A partir de ese momento, si los mensajes no se repiten, el enlace se puede considerar con precisi\u00f3n como unidireccional.<\/p>\n<p lang=\"es-MX\">En un etherchannel UDLD s\u00f3lo act\u00faa sobre el enlace f\u00edsico que detecte unidireccional. Los dem\u00e1s miembros del etherchannel operan normalmente<\/p>\n<p lang=\"es-MX\">Una vez que el modo agresivo UDLD haya puesto un puerto de conmutador en el estado errdisable, debe usar el siguiente comando para volver a habilitarlo:<\/p>\n<pre class=\"height-set:true height:700 width-set:true width:700 top-margin:25 left-set:true left-margin:25 toolbar:2 lang:sh decode:true\">Switch# udld reset<\/pre>\n<p lang=\"es-MX\">El comando anterior reinicia todos los puertos envados a errdisable a trav\u00e9s de UDLD, otra opci\u00f3n es configurar el feature RECOVERY de errdisable para recuperar los puertos cada cierto tiempo.<\/p>\n<p lang=\"es-MX\">UDLD es un feature que se puede utilizar para evitar loops de capa 2 con Spanning-Tree, debido a que STP puede pasar un puerto de estado BLOCKING a FORWARDING debido a un enlace unidreccional, aqui es donde UDLD toma relevancia al mandar a estado errdisable el puerto unidreccional para evitar loops. Tomemos en cuenta que UDLD puede identificar un puerto unidireccional en 45 segundos y STP toma aprximadamente 50 segundos en poner un puerto en FORWARDING.<\/p>\n<p>Mas informaci\u00f3n:<\/p>\n<p><a href=\"https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/switches\/lan\/catalyst3750x_3560x\/software\/release\/15-2_4_e\/configurationguide\/b_1524e_consolidated_3750x_3560x_cg\/b_1524e_consolidated_3750x_3560x_cg_chapter_0100111.html?bookSearch=true\">https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/switches\/lan\/catalyst3750x_3560x\/software\/release\/15-2_4_e\/configurationguide\/b_1524e_consolidated_3750x_3560x_cg\/b_1524e_consolidated_3750x_3560x_cg_chapter_0100111.html?bookSearch=true<\/a><\/p>\n<p>#<\/p>","protected":false},"excerpt":{"rendered":"<p>UDLD is a Cisco proprietary Layer 2 protocol that monitors the state of a port to validate bidirectional communication. Recall that each <\/p>","protected":false},"author":2,"featured_media":1392,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[233],"tags":[280,494,427,493],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v19.13 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>UDLD - UniDirectional Link Detection - JMCristobal<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jmcristobal.com\/es\/2021\/01\/18\/udld\/\" \/>\n<meta property=\"og:locale\" content=\"es_ES\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"UDLD - UniDirectional Link Detection - JMCristobal\" \/>\n<meta property=\"og:description\" content=\"UDLD is a Cisco proprietary Layer 2 protocol that monitors the state of a port to validate bidirectional communication. 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