BGP Routing with Two ISP Providers ( Multihoming) for Load Sharing and WAN Failover

[Yasmeen]

Hi All

      we have one Router and connected with two ISP Providers ( TATA and Airtel), 

      Primary ISP Link - TATA - 100 Mbos 

Secondary ISP link - Airtel - 100 Mbps 

some times any one of our ISP got down due to Outside Issue ( Roads Blocking, Building problems, Road Maintenance reasons ISP Connection in Office WAN Interface )  

Due to Long downtime and productivity issue we plan to configure BGP routing  with ISP Providers and Enterprise Network 

We have collected some points from ISP Providers, 

As of now Airtel Given 

WAN Pool /30 Segment 

LAN Pool /29 Segment 

TATA ISP Given 

LAN and WAN /29 Segment ( Only one Segment Given) 

For BGP routing Configuration Did we need LAN and WAN Segments ?

TATA ISP said that we need to purchase Public ASN Number and /24 Segment LAN Pool from IANA or RIR ?

In this Scenario My query is 

Why Do we Need to purchase Public ASN Number ?

Why not we USE Private ASN for BGP routing between 2 ISP Providers ?

Why do we Need to Purchase /24 Segment LAN Pool from IANA or RIR ?

Why not /29, /28, /27 Segmented LAN Pools ?

Can We Use Airtel given /29 LAN Pool for Both TATA and Airtel ISP Connection ?

Is it Possible to Use One ISP provider given LAN pool to Use in Another ISP Providers ?

Please Let Know ?

Thanks,

Regards,

Yasmeen Shaul Hameed.

[balaji.bandi]

Why Do we Need to purchase Public ASN Number ?

yes if you need Long term Solution to have own AS and own Public IP address space, you can do BGP TE how you want to load share between ISP Like TATA and Airtel.

Why not we USE Private ASN for BGP routing between 2 ISP Providers ?

No you can use Private ASN with Public peering, you have iBGP in your Local side, but as per description you do not need iBGP ( guessing that you do not have mass network ? Do you please confirm ? any network diagram)

Why do we Need to Purchase /24 Segment LAN Pool from IANA or RIR ?

That is minimum they sell as part of AS purchace, you need to contact APNIC

Why not /29, /28, /27 Segmented LAN Pools ?

/24 is minimum buy with AS Purchase.

Other solution if you do not like to buy AS.

You can use  Both provider provide IP address WAN side, and use Local RF1918 IP address space and do NAT.

You can do PBR to use each ISP based on the subnet, and you can track using SLA each ISP and fail over to other ISP. (this most idustry standrd they do)

Until you have any specific requirement LAN segment to be only Public IP - that is different discussion (you need to confirm)

you can aslo do NAT and static nat with Public to Private for LAN IP for incoming traffic, if you have any service hosting ?