Hi,

We are using CCR1036-8G-2S+EM, they support:

• 2 SFP+
  8 GiE

Our uplink with our ISP is using 2 x SFP+ for BPG (bonding interface) to receive 20Gbps. How 20Gbps can distribute traffic to server while it has only 8 GiE.

I see speed test showing support 21333.4Mbps with 64 byte testing: https://mikrotik.com/product/CCR1036-8G ... estresults

Is this the problem in hardware design?

maybe ccr1072 fit better for your interface requirements

https://mikrotik.com/product/CCR1072-1G-8Splus

Is this the problem in hardware design?

No, the problem is that you chose wrong device for your use case.

Throughput tests are done so that ports are used bi-directionally and independently. Which means that diring tests device is routing between both 10Gbps interfaces full-duplex, which means 20Gbps over this pair of ports alone. Add 8x1Gbps full duplex and you see that test result means router can't route full wirespeed, but comes close.
If you use device so that only 1Gbps RJ45 ports are used for downstream, then single 10Gbps upstream port is overkill already.

maybe ccr1072 fit better for your interface requirements

https://mikrotik.com/product/CCR1072-1G-8Splus

i know CCR-1072 model but we are just asking about 1036 design limitation.

Is this the problem in hardware design?

No, the problem is that you chose wrong device for your use case.

Throughput tests are done so that ports are used bi-directionally and independently. Which means that diring tests device is routing between both 10Gbps interfaces full-duplex, which means 20Gbps over this pair of ports alone. Add 8x1Gbps full duplex and you see that test result means router can't route full wirespeed, but comes close.
If you use device so that only 1Gbps RJ45 ports are used for downstream, then single 10Gbps upstream port is overkill already.

Their test showed 20Gbps uplink and 8Gbps downlink (in case we use bonding 2 SFP+). In this case, they can support max 8Gbps only.

Or they can support only 10gbps uplink and 10gbps downlink. No way to handle 20Gbps while their capability showing that they can support more than 20Gbps.

Again: in throughput tests, there is no uplink and downlink, it's traffic between ports, where all connected devices (to all ports) are equal peers communicating between each other.

In your case, however, some devices (clients, those connected to 1Gbps ports) only communicate with devices connected to 10Gbps ports (internet, ISP, whatever) and (most importantly) devices connected to both 10Gbps ports don't communicate through your router. Which then severely limits practical maximum throughput through router in your particular use case .... which doesn't mean device is not capable of higher throughputs in diferent use cases.

Their test showed 20Gbps uplink and 8Gbps downlink (in case we use bonding 2 SFP+). In this case, they can support max 8Gbps only.

Who is "they" and what particular test was it? UDP tests are not really relevant if one does not consider all the facts correctly (most important is to consider numbers on receiving side).