WAN Router

[KESHAV METHI]

                   For CISCO 3-tier hierarchical model(core, distribution, and access layer), where should the WAN routers be connected(whether on core/distribution/ access layer)?

[Sandeep Choudhary]

Hi Keshav,

You can connect 2 FE or GE links from Router  to Core Switch, you can then assign  "portvlanpri" for each these ports on the switch so that the load on  line is distributed over the two, and in case one line fails, the  traffic on that link would anyway switch to the other link.I think , you will use VLAN rtouting on router!

Regards

Please rate if it helps.

[nkarthikeyan]

Hi Keshav,

The layer structure for the architecture you have mentioned is like the below.

Core Layer

  |

Distribution Layer

  |

Access Layer

Access Layer --> This is the layer where you have the actual user / server ports connected to it... i.e. connected to the end user or server to it.

Distribution layer --> This will be layer 3 device where you can have multiple access layer switches connected to it for futher access. It can be a default gateway for all the access layer devices connected to it.

Core layer ---> This would be your LAN end point devivce where you have the wan router will get connected to it. Which can have a direct connectivity with WAN to receive the external routes & advertise internal network to outside.

Please do rate if the given information helps & mark this as answered if your query resolved.

By

Karthik

[Joseph W. Doherty]

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Posting

If a full 3 tier design, often WAN routers are at the "distribution" level.  Sometimes, they might be "core" level.

However, at small branches, they might cover multiple levels, including "access".

[KESHAV METHI]

Thank you Joseph and Karthik. It seems that for a 3 Tier design WAN router can be deployed either on Core layer or Distribution layer. I am still unsure of how to choose between the two.

Further, does the same thing applies to the WLAN controller?

[Sandeep Choudhary]

Hi Keshav,

You can connect WLAN Controller on Core switch.

Just assign the ports in right vlan for the WLC.

just like this:

interface FastEthernet0/17

description *** WLAN Controller, 10.xx.80.1 ***

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 80-82

switchport mode trunk

ip dhcp snooping trust

Regards

Please rate if it helps.

[Harish Balakrishnan]

Hello Keshav,

Usually Distribution is where your L3 interfaces of users ( SVI) are terminated and this seperates the routing domain and switching domain in the network. WLAN is normally considered as wireless distribution.

Again these terminologies can be manipulated in varies design, for example if you have a pretty large campus with many building blocks, we usually setup Building distribution, campus distibution etc.. which all does routing  + switching based on the requirement..

If your customer wants to have seemless L2  wireless roaming across a large network , you can not have your WLAN at the cambus aggregation where we have only routing, Either you need to connect the controller at the distribution side or you have extend you L2 towards aggregation.. so these designs really  vary in customer to customer.

at the bottom line.. yes WAN placed at the core layer of the network, and distributiin seggregates your L3 domain and L2 domain

Hope this helps

Harish.

[KESHAV METHI]

Dear Harish,

Kindly further elaborate the below.

"If your customer wants to have seemless L2  wireless roaming across a large network , you can not have your WLAN at the cambus aggregation where we have only routing, Either you need to connect the controller at the distribution side or you have extend you L2 towards aggregation"

Thanks in advance

Keshav

[Harish Balakrishnan]

Hello keshav,

Lets take an example if you have a large campus with multiple WLAN controllers. Usually we design in such a way that each building distribution will be under a wireless doamin and when  user roam from that controller to another one will be L3 roaming ( different subnet). But some applications doesnt support L3 roaming where we need to have L2 roaming ( same subnet shared across multiple controllers). In that scenario we need to ecxtend our L2 reachability between different distribution switches  and have controllers connected there.. or connect the controller in aggregation switch and exctend L2  vlan till there..

hope I didnt confuse you

Harish.

[nkarthikeyan]

Hi Keshav,

We can have the WLC also can get connected to the distribution segment. Because am referring the distribution segment as the common segment for data/voice/server/wireless..... So your distribution should tell all the internal route advertisements to the core and core which recevies and adversises the internal segmant & external segment as i already mentioned it will be acting as your LAN endpoint.

So when it comes for LAN/WLAN you can restrict or route everything within LAN boundary using your distribution layer.

In a large scale networks we have distribution layer seperated for each segments Data LAN/Wireless LAN/Server LAN....

whether its a wireless network or wired lan network all it wants to be in a architecture to contact outside network with a control and limitations and vice versa in some cases.

For a better design in this architecture... you can have a L2 switch in between WAN towards your core to fullfill the design standards. i.e WAN (Red Zone) to your LAN (Yellow Zone).

Please do rate if the given information helps.

By

Karthik