Routers only know directly Connected ?

erickafabiana · February 2017

I keep hearing the phrase in videos that routers can only see as far as they're directly routes. Does that statement also refers to the fact that a router can only see as far as his "Next Hop IP, local router also ? As I understand that an IP packet must be forwarded to something the router "Knows about" .

dontstop · February 2017

erickafabiana wrote: »

I keep hearing the phrase in videos that routers can only see as far as they're directly routes. Does that statement also refers to the fact that a router can only see as far as his "Next Hop IP, local router also ? As I understand that an IP packet must be forwarded to something the router "Knows about" .

Pretty much yeah. Routers can have routing table entries to networks more than one hop away (configured via static/dynamic routing) but when it comes down to passing the packet along the line the router needs a neighbor it can pass the packet too which is Layer 2 adjacent. So from the perspective of the Router itself, if it's passing everything off to another host on directly connected networks then it cannot see further than it's directly connected network who has a neighbor it knows can deliver it's traffic.

Edit: So above was my original comment but your question got me thinking. Has your videos or text introduced static routing and dynamic routing yet? If they have yet to introduce these concepts I think they might be referring to the fact that a router by it's nature only has the capability to learn it's directly connected networks for addresses configured on interfaces. Trying to make you aware of the fact that without a routing protocol running a router can only route between directly attached networks "out of the box" so to speak. Trying to emphasis the fact that routers need routing protocols in order to "see" more of the Internetwork.

TechGromit · February 2017

I concur, without a routing table, routers only see other routers directly connected to them.

erickafabiana · February 2017

Yes I was watching the CBT Nuggets videos from Jeremy

. I mean technically a router can see more of the internetwork, but he still must forward the ip packet to a directly connected neighbor right ?

erickafabiana · February 2017

dontstop wrote: »

Edit: So above was my original comment but your question got me thinking. Has your videos or text introduced static routing and dynamic routing yet? If they have yet to introduce these concepts I think they might be referring to the fact that a router by it's nature only has the capability to learn it's directly connected networks for addresses configured on interfaces. Trying to make you aware of the fact that without a routing protocol running a router can only route between directly attached networks "out of the box" so to speak. Trying to emphasis the fact that routers need routing protocols in order to "see" more of the Internetwork.

Yes

that's what I was thinking. I mean sure the router learns about other networks, but that's only to ensure that he has a Match for the Destination IP right? The router can still only forward an ip packet to a directly connected neighbor. right ?, I was just confused on the video. I was thinking that a router can only see as far as it's directly connected routes. Which pretty much is true but a router can only forward an ip packet as far as it's directly connected route* also, . Correct me if im wrong

dontstop · February 2017

erickafabiana wrote: »

Yes I was watching the CBT Nuggets videos from Jeremy . I mean technically a router can see more of the internetwork, but he still must forward the ip packet to a directly connected neighbor right ?

Yep! All routes at the end of the day end up relying on a directly connected routes to leave the router. If you think about it, it kind of makes intuitive sense because the packet has to leave an adapter directly connected to the device.

Routers only know directly Connected ?

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